Yes, an NFL player needs a lot of practice to play.
They run drills on whatever positions they play.
An NFL player has to practice because he gets payed to be on an team. Not only that if an player doesn't practice his postion on the team can be taken by another player. Also if the player doesn't practice he's not that different from an free agent.
It is very unlikely for a reserve future player to play.
The player has to pay a $500 fine.
Yes, on the practice squad
NFL player Will Rackley played for Lehigh.
NFL player Will Svitek played for Stanford.
NFL player Will Yeatman played for Maryland.
NFL player Will Ta'ufo'ou played for California.
NFL player Will Pericak played for Colorado.
NFL player Will Beatty played for Connecticut.
NFL player Will Hill played for Florida.