The batter doesn’t know where the knuckleball is going, right? Neither does the catcher. Leads to A LOT more movement - especially awkward movement - for a player that usually is (comparatively) stationary. Catchers tend to get hurt more than other positions, anyway; this just makes it worse.
Catcher is the only position I never played in a game situation (high school ball). Tried it a few times in practice — no thank you. Safer at the hot corner (3rd base), my usual spot.
