Santos had been a promising shortstop but was converted to a pitcher, primarily as a reliever, by the White Sox's director of development, Buddy Bell.
He has a high-velocity fastball that reaches the high 90s, and is known to throw a nasty slider. His changeup and curveball are highly effective, as well.
Since his conversion from a shortstop to a pitcher, he has pitched in two seasons. In 2010 and 2011 combined, he had a win-loss record of 6-7, 31 saves and 148 strikeouts with an ERA of 3.29 in 115 innings pitched.
Santos spent a good amount of time developing in the minor-league system for the White Sox and refined his pitches and mechanics. He advanced through three minor-league levels in 2009 and made his MLB pitching debut in 2010.
The 2011 season with Chicago proved to be a breakout season for Santos. He had a 4-5 record with a 3.55 ERA, and in 35 opportunities he had 30 saves and struck out 92 batters in 63.1 innings.
Sergio Santos is young and hasn't hit his prime just yet. Spring training will further strengthen him and prepare him for what appears to be the most solid-looking pitching staff that Toronto has had in many years.