Man, this pervert picked the WRONG HOUSE to mess with.

A 48-year-old guy named Geoffrey Cassidy was hiding in the bushes outside of a house in Wellington, Florida on Monday, watching a teenage girl in her room.  He had his hand in his pants, but luckily the girl's father was heading out for work and spotted him.

Geoffrey took off running.

But here's what he didn't realize:  That girl's dad is a former Detroit Lion and Tennessee Titan named Tony Beckham, who played from 2002 through 2007.

And Tony was a cornerback, which means it was literally his job to chase people who were running away from him.  People a hell of a lot faster than a 48-year-old peeping Tom.

So Tony easily caught him and held him until the cops got there.  Oh, and somehow Geoffrey wound up with a black eye and a busted lip in the process.

He's been charged with lewd and lascivious behavior.