I also did this once, but not in a crowded bar. In my case, the quarter was knocked into the pocket and the ball went flying off the table so my opponent had no idea what I’d done until I couldn’t stop laughing.
My answer to the OP’s question would be: “unsportsmanlike”
Although more often applied to non-athletic games, “sandbagging” is another term that may apply to one particular form. This is where you misrepresent your abilities or situation so as to make your opponent drop their guard, or up their stakes. The classic pool hustle is a form of this - you play shitty until somebody makes a sizeable enough bet, then you take them to the cleaners. It can also be used in various “win by losing” situations. I became well acquainted with the concept as a kid by losing at Gin Rummy to my uncle.
Putting an obstruction on the table is not “dirty pool”, it is “blatently against the rules” of pool.
In business we call it “thinking outside the box”.
Joseph Campbell used the following in discussing ethics.
In American sports there are rules to cover almost every possibility. However, there are very few rules that govern rugby in England. Two Americans went to Britain during the early part of the last century and soon their team was winning all of their rugby games. These two were using the forward pass which had just become popular in American football. After a few games the British students went to these two and explained that even though there was not a rule against it, they just did not use the forward pass. It was stopped not because of a rule against it, but because it was unethical.
There was a video fighting game that used to display a hunk of “cheese” when a player would over-use any one move, after that, the “cheesy” player would start taking damage when over-using that same move.
I call people who do that sort of thing either cheap, or lame. Most times, such play is considered underhanded, but sometimes it makes things more interesting. Very subjective.
I believe the behaviour might be described as unchivalrous, although the term encompasses a rather broader spectrum of ungentlemanly actions than just unsportsmanlike stuff in duels etc.
I don’t know if the original question was ever answered, but one example was the “fumblerooski” that was once used in college football. Since then (mid 80s?) I think the rules have been changed since to make it illegal.
Basically it involved a QB placing the football underneath a guard, technically making it a fumble. The QB then draws back, as if he still has the football, while the guard, who would typically never handle the ball, lumbers forward.
Sandbagging is sometimes done (or alleged) in handicap league bowling. Handicap uses your average score to add points to lower averaged bowlers, evening out different skill levels. If you were way ahead and purposefully bowled lousy to keep your average down, that’s sandbagging, very much frowned upon.
Gamesmanship, I always thought of it as more clever and crafty than dirty or cheap play. I think unsportsmanlike fits, though it has other connotations as well.
Scratching on purpose in pool, I think of that as dirty play. As far as playing the game goes, that strategy is no more fun than just having your opponent rack up all the balls and say “you win”.
Here in the US, “cheesy” or “cheese” is also used in the world of Games Workshop’s hobby games (like Warhammer or Warhammer 40,000 to mean someone who, while adhering strictly to the letter of the rules has skirted their intent or stretched the limits of game balance by employing unorthodox tactics or army composition purely to exploit an opponent’s weakness.
One such tactic, for example, is called “min/maxing,” where the player will compose his army of the maximum number of minimally sized squads of soldiers because he knows each squad may only be issued one or two squad support weapons, then relying on said weaponry to lay waste to the opponent’s forces instead of trying to achieve the objective of the particular match; thus winning by default.
The equivalent term on the opposite side of the pond (i.e. the UK) is “beardy.”