cut fastball

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A fastball released with most pressure from the tip of the middle finger so that it breaks slightly in the manner of a curve ball as it approaches the plate.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun baseball A pitch thrown with an offset grip and a moderate amount of added pressure by middle finger yielding a combination of backspin and some sidespin, resulting in motion to the left when thrown by a right handed pitcher with velocity only slightly diminished from that of a fastball