Bilz
Superstar
most terrible free throw shooters do. shaq used to hit 80% of his free throws in practice, ben wallace couldn't miss free throws in practice either. once gametime comes that mental block hits.
They also don't practice them right. Shooting 200 straight free throws in practice is pretty useless. It's a lot easier to replicate form and gives them a false sense of confidence that they're improving.
In a game situation, they won't get to just stand there and shoot 50 in a row. They'll shoot 2, run up and down the court 20 times, then shoot 2 more. They need to be practicing their shot all the time just like other players do so its a natural situation to walk into.