Once a model has been created, it is not as simple as just letting it sit and make predictions over time. Even if none of the inputs into the model are updated, it’s important to continue to retrain models on more up to date data, as MLB and baseball in general is constantly changing.
In the case of a stuff model, as soon as strides are made from pitchers to find an edge, hitters begin adapting to it. The best recent example of this is the sweeper. Partially due to the rise in prominence of stuff models, the sweeper began gaining traction a few years ago as an elite pitch shape, specifically against same-handed batters.
The sweeper has been an incredibly effective pitch to generate whiffs. In 2021 sweepers generated the second highest whiff percentage of all pitch types, behind only the splitter. It was after this season that sweeper usage really ticked up, but as of 2024, sweepers are now generating whiffs at rates comparable to changeups and curveballs.
