A female pitcher that comes in as a late reliever. Pitches maybe an inning.

MLB hitters, under regular, consistent circumstances would be able to deal with an underhand pitch. However, that's under consistent circumstances. If she in to pitch for maybe a few batters, few hitters would have the ability to adjust to her, and then adjust back to whatever closer came in after. The whole point would be for her to go in and not consistently see the same hitters over and over. It could be enough to get a few outs.