Unhittable. Hitters are simply guessing and deciding to swing before the ball is even thrown. Devastating pitch... that likely was illegal... but even the announcers are commenting on the expertise scuffing of the ball, so it was likely well known at the time and nobody really cared (much like sign stealing...)
Watch game 2, there was no sign stealing, and then switch to game 7 and watch the Dodgers get slapped around in their own stadium