It's not all that easy to make the transition from the football field to the wrestling ring. Just ask former NFL great Shawne Merriman. Last year, "Lights Out" revealed that he was going to start training to become a WWE wrestler. But a short time after he began trying to launch his wrestling career, the WWE reportedly parted ways with him. It's a little bit unclear where he stands with the WWE right now, but at this point, there's a pretty good chance that his pro wrestling career won't ever take off.

Other former pro football players have found success in the world of pro wrestling, though. For example, "Hacksaw" Jim Duggan—who turns 61 today—spent his college days playing football for Southern Methodist University before signing with the Falcons in the late 1970s. But when his NFL career didn't pan out due to lingering knee issues, he decided to become a wrestler, and it was one of the best decisions he ever made. He spent more than 30 years wrestling professionally, was eventually inducted into the WWE Hall of Fame, and is currently signed to a WWE Legends contract.

Duggan's success got us to thinking about other pro football players who have successfully made the jump from the gridiron to the squared circle. So to celebrate his birthday, we went about Ranking the 25 Best Pro Football Players Turned Wrestlers. Let's get ready to rumble.