I'm not a baseball ump and all I have to go on is what was discussed by the game announcers, so please be patient
White Sox vs Angels. Sox in the field, Angels have runners on 1st and 2nd.
Sox first basement is not holding the runner on 1st and is in front of the runner. They are both a good six or so feet off the bag.
Pitcher comes set and then throws toward 1st with no one covering. The 1st basemen catches the ball and makes a swipe tag and narrowly misses the runner. 1st base ump called a balk. Robin Ventura comes out of the Sox dugout, argues and gets tossed.
The announcers were surmising that you can't throw to an unoccupied bag, or some such discussion. There didn't appear to be any talk on the field about the pitchers foot, angle, or the move.
Thoughts? Rule? Announcers crazy? Not enough info? It was odd, as it was a close play.
Thanks.