With the consent of a single justice of the Supreme Judicial Court, the Commonwealth brings this interlocutory appeal from a Superior Court judge’s allowance of a motion to suppress evidence. See Mass.R.Crim.P. 15(a)(2), as appearing in 422 Mass. 1501 (1996). At issue is whether police acted permis*641sibly in stopping the defendant to conduct a patfrisk, in response to a telephonic tip that a teenager at an outdoor basketball game had lifted his shirt, revealing a gun underneath. We reverse the order allowing the motion to suppress.

Summary of facts and proceedings. We summarize the facts found by the motion judge, supplementing those findings with additional, uncontested background details from the record. Just before 7:30 p.m. on August 1, 2002, a State police emergency operator took a call placed by cellular telephone (cell phone) from an unidentified citizen. The State police system involved can identify a cell phone number, but not the name or exact location of the caller. The caller reported that she was at a park on the comer of Columbia and Washington Streets in Cambridge and had “just seen a kid with a gun underneath his T-shirt.” The operator connected the female caller to the city of Cambridge 911 operator, Anneta Penta, stating, “I have a cell phone number of [telephone number], Ma’am, are you still on the fine?” The caller said, “yes.” Penta stated that the call was being recorded and asked her to describe the emergency. The caller again gave her location in Cambridge and said that she was at a basketball game. She said that she had “just seen one of the teenagers lift his shirt and seen a pistol in his pants.” The caller described the teenager as wearing dungarees with red trim, a black shirt, and a blue baseball hat with red trim, and said that he was standing behind a car “on the corner of Columbia and Washington right now as I am talking to you and I just [inaudible] so when you all roll up there he’ll know that I’m the one that called okay?” The caller could not identify the type of gun; Penta terminated the call and immediately dispatched the information to two units that responded to the call.

Cambridge police Officer Michael Regal1 was nearby in a vehicle and arrived first. He testified that the location was called Columbia Park, Area 4, and had “always been a high crime area,” where there was a lot of drag activity and where shootings had occurred in the past. Arriving at the scene within one and one-half minutes, Officer Regal observed three black *642males standing together near a fence at the comer of the park. One appeared to Officer Regal to be much younger than the others, seventeen or eighteen years old, nineteen at most2; the other two appeared to be at least twenty-five. The apparent teenager, later identified as the defendant, was wearing clothing fitting the description that Officer Regal had just heard via radio dispatch. The blue jeans worn by the other two did not have a red stripe, and their hats were of a different color. There were other people in the area watching the game, including families with children. Officer Regal got out of his vehicle and walked up to the defendant, ordering him not to move. He spread the defendant’s arms and conducted a patfrisk; Officer Regal felt a hard, rough handle protrading from the waistband of the defendant’s pants, which he thought might be a gun and which he removed. The object was a .22 caliber handgun, with one round in the chamber; the hammer was cocked and it was ready to be fired. As Officer Regal was conducting his inquiry, other officers arrived and confirmed that the defendant did not have a license to possess the gun. The defendant was arrested and taken to the police station. An officer conducting an inventory of the police van that transported the defendant to the station found cash and what appeared to be a quantity of cocaine in several packages.

Thereafter, the defendant was indicted for possessing cocaine with the intent to distribute, second offense; doing so within one hundred feet of a public park; unlawful possession of a firearm, second offense; and possession of a firearm with a defaced serial number while committing a felony. The defendant moved to suppress the handgun, ammunition, fifteen pieces of (alleged) “crack” cocaine, a cell phone, a beeper, a wallet, and seventy dollars in cash. Following a hearing, the motion was denied and the defendant filed an application for interlocutory appeal. The Commonwealth opposed the application and filed a motion to supplement the evidence that had been presented at the hearing on the motion to suppress. This motion was al*643lowed, and after a further evidentiary hearing, the defendant’s motion to suppress was allowed.3 The Commonwealth was given leave to file this interlocutory appeal from that ruling.

Discussion. “In reviewing a ruling on a motion to suppress, we accept the judge’s subsidiary findings of fact absent clear error ‘but conduct an independent review of [her] ultimate findings and conclusions of law.’ ” Commonwealth v. Scott, 440 Mass. 642, 646 (2004), quoting from Commonwealth v. Jimenez, 438 Mass. 213, 218 (2002). “Where police conduct an investigatory stop based on information gleaned from an anonymous tip, courts assess the sufficiency of the information in terms of the reliability of the informant and his or her basis of knowledge. . . . Where the information relied on to establish reasonable suspicion is transmitted by radio bulletin, both the source of the information and the basis of the source’s knowledge must be demonstrated to be reliable.” Commonwealth v. Walker, 443 Mass. 867, 872, cert. denied, 126 S. Ct. 662 (2005).

Police officers may act on the basis of a citizen report of apparent breaches of the peace that the citizen has observed, i.e., a tip, when the citizen has identified herself or has placed her anonymity at risk. The applicable law has been recently restated in Commonwealth v. Love, 56 Mass. App. Ct. 229, 233-234 (2002), where we said that “[t]he face-to-face character of the citizen witness’s contact with the police is significant, but it is not dispositive: if an in-person informant declines to identify himself, his report remains subject to the greater scrutiny given anonymous tips. . . . The guiding principle is whether the informant ‘places his anonymity at risk.’ Grasso & McEvoy, Suppression Matters Under Massachusetts Law § 4-3(c)(2), at 4-26 (2001). If so, ‘a court can consider this factor in weighing the reliability of the tip.’ Ibid.” (Footnote omitted.) Cf. Commonwealth v. Cox, 56 Mass. App. Ct. 907, 909 (2002).

*644In this case, the number of the cell phone from which the citizen caller had placed her call was identified by the State police system, repeated out loud while the caller was on the line, and recorded. The citizen caller was not asked to identify herself; she did, however, give her location as standing close to the defendant, such that he might know she was placing the call if police arrived immediately on the scene. The caller placed her anonymity at risk, because the cell phone number could have been traced to the owner of the cell phone; she also was standing near the defendant as she placed the call, and police could have questioned those nearby had they wished to identify the caller. See Commonwealth v. Stoute, 422 Mass. 782, 790-791 (1996) (information “provided by bystanders who could have been identified”).

Even if the caller had borrowed the cell phone in order to place the call, she was potentially traceable through the owner of the cell phone. See, e.g., Commonwealth v. Love, supra at 230-232, 234 (where the citizen witness was a passenger in a car, the license plate number of which was recorded by a desk officer, the witness was “identifiable if not identified,” and “potentially traceable”). This was not a “bare report of an unknown, unaccountable informant” as to which police were without the means to test the informant’s basis of knowledge or credibility. Florida v. J.L., 529 U.S. 266, 271 (2000).4 As Justice Kennedy noted in his concurring opinion, the anonymous telephone tip in Florida v. J.L. did not justify a stop and frisk because the “record [did] not show whether some notation or other documentation of the call was made either by a voice rec*645ording or tracing the call to a telephone number.” Id. at 275 (Kennedy, J., concurring). Moreover, unlike in Florida v. J.L., here police response to the call was immediate.5 The fact that in the instant case a record was made of the call is also significant in that it “eliminat[es] the possibility of a police fabrication which is a principal concern in assessing the propriety of a threshold inquiry launched by an anonymous tip.” Commonwealth v. Lyons, 409 Mass. 16, 20 (1990), quoting from Commonwealth v. Anderson, 366 Mass. 394, 399 (1974).

The caller in this case described a crime in progress — a teenager was in possession of, and displaying, a gun.6 The circumstances required an immediate response from police, as the teenager was at a basketball game being attended by families, including children; police knew the location to be a high crime area where shootings had occurred in the past. Officer Regal, who was at the scene within one and one-half minutes, saw a teenager at the location described by the caller, wearing clothes that fit the description. At the time Officer Regal stopped the defendant, he had an objectively reasonable suspicion, based on specific, articulable facts, that the defendant was unlawfully carrying a firearm, see Commonwealth v. Lyons, 409 Mass. at 19, and displaying that firearm in a crowded venue. See Commonwealth v. Foster, 48 Mass. App. Ct. 671, 676-677 (2000) (officers with experience of shootings during after-hours parties on Armandine Street received information from a known bystander who, they could have inferred, had personal knowledge that one of the men seen on Armandine Street was *646displaying a gun; officers acted reasonably when they pat frisked the men, believing them to be armed and dangerous), and cases cited therein.

Conclusion. Based on the foregoing, the order of the Superior Court allowing the motion to suppress evidence obtained in the investigatory stop is reversed.

So ordered.