It's Always Sunny in Philadelphia: Season 2, Episode 1

2 - 1: Charlie Gets Crippled

Dennis and Dee's estranged father, Frank Reynolds (Danny DeVito), returns to town to reconnect with his kids. They don't want anything to do with him, but Frank likes hanging with Charlie and Mac. Meanwhile, Charlie gets hit by Dennis's car (accidentally, of course) and needs to use a wheelchair. The gang soon discovers that this isn't all that bad.