eephus
An off-speed pitch with unusually low velocity, intended to catch the hitter off guard.
Sewell was determined to live or die by the eephus.
Where it comes from
The naming of the pitch is generally credited to Maurice Van Robays in 1942, who said "it's a nothin' pitch, and eephus ain't nothing'". However, it is not clear what the source for the name is; possibly Hebrew אפס (“nothing, zero”).
Adapted from the Wiktionary entry eephus (CC BY-SA 4.0).