OPS against is a stat for pitchers. In the standard baseball OPS meaning, batters want the number to be his, OPS against is the OPS a pitcher gives away to betters. Because of this, pitchers want their OPS against to be low. Baseball is one of the hardest sports to predict, and therefore wager on. The old adage that “momentum is only as good as tomorrow’s starting pitcher” is accurate, which can mitigate trends. For instance, if a player has a four-hit game against a mediocre pitcher, he may struggle the next day against a star-caliber starter, which makes wagering on player props feel like rolling a dice. But there are predictive MLB stats, and arguably the most important for hitters is OPS — or On-base plus slugging.