According to the New York Times, "Luis Arroyo, a stoutly built left-hander with a baffling screwball who was an All-Star in each major league, pitched in two World Series and as a reliever helped Whitey Ford achieve his finest season with the Yankees, died on Wednesday in Guayanilla, P.R. He was 88. His daughter, Milagros, said the cause was cancer.
Over all, Arroyo had a middling career, spending all or part of eight seasons in the major leagues with four different teams. But in 1961 he was the best reliever in the game, a prototype of the late-inning specialist now known as a closer."
Arroyo developed that screwball with the Yankees.
The New York Times also had a great quote from Casey Stengel in reference to Arroyo:
“They say he don’t look much like a pitcher... Then again they say Yogi Berra don’t look much like a ballplayer.”
Luis Arroyo. Dead at 88.