It's a shark tactic -> sometimes used on purpose, but mostly used by novice players unwittingly. In most places, any such tactic (e.g., moving toward the table, grabbing the rack, and pulling balls) is an automatic concession.
The only rule I know of is breaking your cue down = a concession.
WPA rules have this implemented (for tourneys at least).Some leagues use this
rule as well.
The counter to this is that some rules do not allow concessions in any way. Giving one results in loss of that game PLUS the loss of another game... Two players agreeing to concessions can be DQ'd from the tourney.
But, I have no idea how any of this applies in league play, but I think your unsportsman like conduct comment is spot on.
-td