Regardless, only 'jeff0120' came the closest getting the first two but missing the third (right idea....wrong player)
The clues....'head scratcher' and 'aren't too sharp' as well as all three being out of the game right now.
You guessed it - all of them have had their bells rung. Concussions are the common thread.
Here are the names that go with the signatures.
Better luck next time!