This article is part of our The Z Files series.
Increased use of advanced metrics for fantasy baseball analysis is obviously great. However, there's a downside. As more incorporate the data into their work, pressure mounts for others to follow suit. Unfortunately, the repercussion is not everyone fully understands the derivation and application of all that's out there, resulting in misuse.
A prime example of this is the expected Statcast stats, such as xBA (batting average), wSLG (slugging percentage) and xwOBA (weighted on base average). It's become commonplace to compare actual results to expected, looking for significant deltas. An actual stat higher than expected is often deemed lucky, and vice versa. On the surface, this makes sense. However, there's a major flaw in that reasoning.
Statcast deploys a unique means of measuring hit probability. In short, the components (exit velocity, launch angle, sprint speed, etc.) are compared to a database of similar batted ball outcomes and assigned a hit probability. What percentage of similarly batted balls are hits? What is the distribution in terms of single, double, triple and homer?
By means of example, if a specific batted ball was a hit 50 percent or the time, it counts as 0.5 hits and gets included in xBA as such. If it cleared the fence 10 percent of the time, it's logged at 0.1 HR and gets factored into xSLG, xwOBA etc, in that manner.
Missing from the above description is park influences. The same traits could be a homer 80 percent of the time in Yankee Stadium only to be