Calling a balk on a 3rd baseman...

[ElPanadero]

Can you call a balk on a 3rd baseman?

Here's the situtation: bases loaded in the bottom of the extra inning of a 5-5 Mustang game (9 & 10 year olds). The batter has 2 strikes on him and there are 2 outs. The pitcher throws a called 3rd strike, batters out, 3rd out and the game ends in a tie.

Not so fast...the base umpire calls a balk on the 3rd baseman for straddling the foul line. One foot is in fair territory and the other foot is in foul territory while he is trying to hold the runner. The manager of the other team had already given the base umpire a heads up and pointed out that the 3rd baseman had been doing this the whole game.

There was no attempted pick-off at 3rd during the last pitch. The game ends in a 6-5 win for the home team (who was at bat) when the winning run is balked in.

Can you even call a balk on anyone besides the pitcher and catcher. Is that a correct call? I referenced OML baseball rule 4.03 and think I figured it out. Not sure though. Any help would be appreciated.