legal tag?

[JJ]

Had a partner get into a good discussion on a similar play - runners on first and second, nobody out, looper to center that is short-hopped by the fielder (no catch). He throws the ball to third ahead of the sliding runner, the umpire watches the play and calls, "SAFE!". Coach comes out and says, "Why?". Umpire replies, "He got in under the tag." Coach then says, "But he was kneeling on the bag when the runner slid in, and it was a force out." Umpire looked confused, listened to his rear being chewed awhile but did not eject the coach, and ultimately learned to watch the whole play from then on. The safe call, right or wrong, stood. I did say it was a partner, didn't I? Yeah, that's it. A partner...