Not long ago, Denard Span looked like nothing more than a grade C prospect who failed to make good on his tremendous athletic ability. Then, something changed, and quickly. Span developed a more patient approach at the plate, which led to him drawing more walks and getting better pitches to hit. Fast-forwarding to today, Span is an extremely valuable regular on a winning team. Breakouts can seemingly come from out of nowhere, but there are statistical indicators that tell us which are more real than others.
Naturally, at this time of the year we view players with a certain air of suspicion, and rightly so; Small sample sizes make trusting early season statistics difficult. However, there is a point in time when certain stats can become more trustworthy than others. A study done by Russell Carlton showed that after 50 plate appearances, a player's swing habits can be a reliable guide to what's going on. In the case of Colby Rasmus, his swing habits give us a substantial reason to believe he's a changed man. According to O-Swing percentage (which is a stat we use at FanGraphs that measures the percentage of swings a batter takes at pitches outside of the strike zone), undisciplined batters greatly decrease their odds of reaching base by mercilessly hacking at everything thrown their direction. (This shouldn't surprise anyone.) Rasmus did not really show great plate discipline last season, evidenced by a paltry .307 on-base percentage. He swung at 25.9 percent of pitches thrown out of the zone last year, but this season, he's decreased that number to just 17.8 percent. As a result, Rasmus has drawn more walks (17) than teammate Albert Pujols (15) and he's taking more advantage of pitches he's finding to his liking. The result? A line of .316/.436/.658. People have projected stardom for Rasmus since he was a first-round pick in 2005, and it appears the 23-year-old is figuring things out.
Like Rasmus, Oakland's Daric Barton is also demonstrating a tremendous amount of selectivity at the plate, with an O-Swing percentage of just 13 percent. Barton's been known for this for a while, but he is also making a lot more contact when he does swing. He's getting the bat on the ball 89.7 percent of the time when he swings, a 4.8 percent increase over his career rates. When you're not swinging at a lot of bad pitches, and making that much contact with the pitches you do swing at, good things are bound to happen, and they are so far for Barton. He's never going to hit for a ton of power, but he has a .407 OBP and should be an on-base machine for years to come.
Chicago Cubs left-handed reliever Sean Marshall is another breakout to believe in. In the early goings of the season, we see that his curve has about 2 more inches of downward movement according to Pitch f/x data, and he's throwing his curve 41.5 percent of the time. Batters against Marshall have an O-Swing percentage of 33.0 this season, and his career rate is 23.0. Translation: He's getting a lot more guys to chase out of the zone, because he's throwing a curve with more movement. While he's not going to be confused with a flamethrower anytime soon, his average fastball velocity is up from 87 mph to 89.3 mph, a considerable increase. A better fastball helps set up the off-speed, and it helps when that off-speed pitch is a filthy, knee-buckling curveball like Marshall's. He's fanned 18 and walked just two batters in 14 innings, and his dominance could give the Cubs the flexibility to move Carlos Zambrano back into the rotation.
Erik Manning is a writer for FanGraphs.