It doesn't look pretty but it gets the job done. Big time. That's what I can say about Alfonso Soriano's throwing arm in left field. He throws like the former second baseman that he is. It's that side-arm throw that all second baseman master to get their throws over to first base quickly. And that's what Soriano does in left field. That's part of the reason it's so successful; he gets rid of the ball quickly. There are two more reasons why he is so good: His great speed allows him to get to the ball quickly before making a throw, and he is incredibly dead-on accurate.
At the beginning of the 2006 season, Soriano was reluctant to move to left field after having played second base his entire career. He even refused to take the field in his first spring training game as a left fielder. But he finally agreed to play and he took to playing the outfield, particularly left field, like a duck to water. After a bit of an adjustment period, he became a very good outfielder. But it's his throwing that has really stood out.
How deadly has he been? In 2006, he had 15 baserunner kills (a direct throw to a base to "kill" a baserunner—no relay involved) in left field. The next best left fielders had 10 (Craig Monroe and Raul Ibanez). He got even better in 2007. He had 19 baserunner kills while the next best left fielder had 7 (Jason Bay).