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A man wearing batman underwear and a cape ran onto the field at Baltimore's Camden Yards during last Friday's opening game, and a second man invaded the field on Tuesday. Both were subsequently banned from the stadium for life. Dozens of other fans have been prohibited from entering sports arenas nationwide for similar acts over the years. How are such bans enforced?

They're not. Stadium security personnel are tight-lipped about their procedures, but people in the industry say that little is done to prevent banned spectators from entering U.S. arenas. Some teams may stop rule-breakers from buying tickets online, but that wouldn’t interfere with their acquiring tickets through friends or scalpers and entering the stadium anonymously. A "lifetime ban" simply makes it easier to prosecute a repeat offender. The team wouldn’t have to prove that the suspect instigated a fight or threw something on the field, because his mere presence in the stadium would constitute trespassing.

A handful of European stadiums have deployed newer video technologies to keep out banned spectators. Parking lot entrances provide the first line of defense, with cameras set up to screen license plates in real time. Digital cameras mounted at the turnstiles, paired with facial recognition software, can identify banned spectators as they enter the stadium proper. If security misses a trespasser at the gate, they may be able to get him at his seat. It only takes 10 to 12 high-tech cameras to monitor a 50,000-seat stadium with sufficient resolution to identify individual spectators with reasonable reliability. Of course, it’s easy enough to defeat the facial recognition analysis with a pair of sunglasses and a baseball cap. Stadium owners who are really serious about barring miscreants, however, force spectators to remove such accessories as they pass through the gate. The process isn’t 100 percent effective, but violators are caught with some regularity...
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So the same technology used to control inmates in prison is now being used to keep the rest of us in line too!