It’s not unusual for crowds of teenagers to gather on Broad Street just south of Temple University’s campus — the movie theater on Oxford Street means kids often hang outside on the weekends, waiting to meet friends or milling around after a film.

But the crowd Friday night — about 200 youths who organized a “meet-up” on Instagram — was unusual, said Charles Leone, Temple’s director of public safety. Around 8:30, a few dozen kids broke into groups and spent the next hour or so wreaking havoc within a seven-block radius.

Four youths were arrested after two students and their friend were assaulted, a police officer was knocked off his bike, and a police horse was punched in the head.

In the aftermath, some students complained that the university had not alerted students quickly or accurately enough. A text alert about “large groups of juveniles along Broad Street” was sent around 9:30 p.m. but did not mention the assaults. The school sent out a long email Monday detailing the incident.

Deciding how and when to warn students about incidents on campuses is a surprisingly complicated task. Notifications of potential danger vary widely among colleges around the country -- and it's a process that Temple has been tweaking for years. In light of what happened Friday night, Leone said, officials will tweak it again.

Universities are required by federal law to alert students about on-campus crime. The Clery Act is named for a 19-year-old Lehigh University student murdered in her dorm in 1986. After her death, Jeanne Clery’s parents fought for a law that obligated schools to publicly report crimes on campus, arguing that she would not have gone to Lehigh had she known about the school’s crime rate at the time.

In practice, this means colleges have to publish crime reports every year, but they also have to issue “timely warnings” to students after certain kinds of crimes occur on campus — homicide, rape, robbery, hate crimes, and a slew of other offenses.

But the act doesn’t define timely. The kinds of crimes a university chooses to alert students about can vary, too.

“A warning should be issued as soon as pertinent information is available… even if you don’t have all of the facts surrounding a criminal incident that represents a serious and continuing threat,” the Department of Education wrote in a handbook on campus safety this year.

Drexel University’s Department of Public Safety has  “a comprehensive list of emergency scenarios” that could trigger an alert, according to its website, including “an armed suspect on the loose” or a bomb threat. The University of Pennsylvania says on its website that it sends out alerts in case of a “major emergency.” Some recent alerts have included two unarmed robberies and a test of the campus’s shelter-in-place system.

"The real key here is that purpose of an alert is not a news source but a public safety directive — asking people to change a behavior," said Sarah Powell, Temple's director of emergency management. "If some kind of incident occurs but no change of behavior is required, we won't send an alert out."

So a school might choose to send out a text alert for a crime that isn't covered under the Clery Act — or warn students about, say, a rash of robberies just off campus, even though the area isn't covered by campus police.

Or they might not. Several area schools have fielded criticism in recent years for not sending alerts on certain crimes or not sending them fast enough. (“It’s rare that I hear people ask, ‘Why did you send that alert?’” Leone said.)

A Daily News report in 2014 noted that after a Temple student was hit in the face with a brick a block off campus, the university did not issue a statement on the incident for three days. The newspaper found that Penn and La Salle University did not send alerts about two violent crimes involving students that took place off campus in the last several years.

That’s all technically within the parameters of the Clery Act — as the crimes took place off campus.

Since the brick incident, Leone said, Temple expanded the area that it sends alerts about by 20 blocks. It also expanded its campus police patrols. As a result, in the last two years, Temple has doubled the number of alerts it sends to students — some 40 alerts have already been sent this year, Leone said. About 80 percent of those alerts are for incidents that took place off campus, he said.

“We’ve worked really hard to create more speed and efficiency in our process,” said Powell. “In the last year, especially, that's really been the case — and the only times where there's a lot more discussion and delay is where it's a novel situation or something we haven't seen before.”

On Friday night, Leone said, the first arrests took place around 8:30, when police took two juveniles into custody for assaulting two students and a friend walking with them.

“Was the threat still active?” Leone said. “We had a threat, but the threat was stopped when the arrest was made. And then we started getting other reports. Then we realized we had to get the information out.”

Leone said his department is working to streamline the process for sending out alerts for incidents like Friday’s. Dispatchers are trained to identify common crimes that would warrant an alert — for example, armed-robbery alerts get sent out pretty quickly, Leone said.

The school has never sent out an alert for a situation like Friday night’s, though, and couldn’t rely on the standard script for an armed robbery or a shelter-in-place alert.

“Most people think everything happens in one confined area --and we were getting reports from several blocks, pulling this all together. Once we saw a pattern forming, saw these violent acts,” it was decided to send the alert out, Leone said. And then officials had to figure out what to say -- in 160 characters for a text message.

“We’re trying to figure out how to do better, how we can improve even more so with unusual events,” he said, “so if something like this should arrive, we don’t have to get involved with scripting language.”