Sports term for any kind of injury that has you lying on the playing surface for an extended amount of time, and the announcers aren't quite sure of the exact cause yet. You can be shaken up after a concussion (after which you "shake out the cobwebs"), whiplash, a broken bone, a torn ligament, a deep contusion, a hit to the groin, or even simply "getting the wind knocked out of you." Until the cause and/or severity of the injury is known, the announcers will just say that you're "a little shaken up on the play".
"And John, it looks like Steve Young is a little shaken up after the play..." "Yeah Pat, that linebacker hit him and it was like BOOM! Tough Actin' Tinactin!"
"Oh, and Lindros appears to be shaken up after that hard hit by Stevens..."