Were you at that game? This exact thing happened to me 2-3 seasons ago; LL post-season tournament, Majors (12U) game. I'm PU; game is tied in the bottom of the 6th; R1 & R3 - 2 outs. My partner has warned F3's & F5's on both teams several times to keep both feet in fair territory while holding the runners (I know! I don't pick that scab unless I absolutely have to) As F1 throws, I hear 'Time! That's a balk! You - score." I waited at the plate for a moment to see if either manager was going to say anything, but . . . . . nothing.
So - we left the field. When I explained to my partner that there's no such call in LL (didn't bother to address calling 'Time' first) he said, "Well, I had warned them, so I don't feel bad about it." And, he didn't, either.
I saw it happen in a 12U Major game last month in the Kansas City area. Head coach called the issue to the BU's attention when it happened earlier in the game, but apparently convinced him to save the "call" for later when his team needed it most. Total horse----.
"Don't do it," was the appropriate way to address the situation. If coaches continue to complain about it, and the defense continues to do it while completely disregarding warnings, then, at MOST, your partner may have had an ejection situation for the offender(s). Never seen it get that far, though.