A Sprinkler is a kind of participant or gambler in a game of casino Roulette. This person generally places large bets on any of the 38 numbers on the game layout, whose betting style depends only on luck, rather than applying any understanding of the game, knowledge, logic or methodology / systematics. The sprinkler approach to the game may yield a quick pay-off in the short-term, but such an inexperienced approach to the game will result in more trips to the ATM to stay in the game. Incidentally, the casinos just love these kinds of people (accounting for a majority of gamblers).
"This gambler is really a numbskull. She just placed $5 on 20 numbers, but she did not win. Quite a sprinkler, she is."