Not so long ago, Brandon Belt was the "neglected middle child" of the Giants' system. Despite sterling numbers at every rung of the minor leagues, Belt was promoted haltingly and not given consistent playing time by manager Bruce Bochy. The nadir came when Belt, not long into the 2011 season, was benched in favor of the smoldering ruins of Aubrey Huff. Time in left field followed for Belt, but then a trade for Melky Cabrera relegated him to the farm once more.
In 2012, Belt finally got something close to regular playing time (although it wasn't until June that he became a fixture at first base), and he responded with a solid age-24 season: .275/.360/.421 (123 OPS+).
This season, Belt is on pace to log a qualifying number of plate appearances for the first time in his career, and, in a possibly related matter, he's also putting up some quietly excellent numbers. In 123 games, Belt has authored a slash line of .279/.354/.478 with 15 homers and 28 doubles. Furthermore, as his excellent 2013 OPS+ of 140 reflects (a mark that's good for eighth in the National League), AT&T Park is a fairly brutal environment for hitters. To put a finer point on it, Belt this season on the road is batting a robust .284/.362/.521. Belt's unadjusted numbers are strong, but only when you correct for his home park will you see how good he's really been in 2013.
So how's Belt doing it? The numbers found on his FanGraphs page provide some insight. First, Belt is hitting more balls in the air this season versus last, and a higher percentage of those fly balls are leaving the park. When you see large spikes in a hitter's HR/fly-ball percentage this can indicate random variation (although that's more the case with pitchers). Still, Belt is a hitter who posted a career ISO of .253 in the minors -- i.e., he has the raw power to justify the increase in his HR/fly-ball rate.
As well, Belt in 2013 can be characterized as "appropriately aggressive." He's roughly league-average in terms of swinging at pitches outside of the strike zone, but when he sees a pitch in the zone, he attacks it: he swings at 79.0 percent of strikes versus a league average of 65.4 percent. That's in line with what Belt did last season, so recognizing strikes seems to be a repeatable skill of his. And when he does swing at strikes, he's ahead of the league mean in terms of how often he makes contact.
In addition to having a good idea of the zone, Belt's also showing strong pitch-recognition skills. Check out this summary of Belt's 2013 season from the indispensible Brooks Baseball:
Against All Fastballs (1,142 seen), he has had an exceptionally good eye (1.58 d'; 86% swing rate at pitches in the zone vs. 31% swing rate at pitches out of the zone) and an exceptionally aggressive approach at the plate (-0.30 c) with a league average likelihood to swing and miss (16% whiff/swing).
Against Breaking Pitches (505 seen), he has had a good eye (0.85 d'; 67% swing rate at pitches in the zone vs. 34% swing rate at pitches out of the zone) and a steady approach at the plate (-0.02 c) with an above average likelihood to swing and miss (36% whiff/swing).
Against Offspeed Pitches (218 seen), he has had an exceptionally good eye (1.52 d'; 91% swing rate at pitches in the zone vs. 42% swing rate at pitches out of the zone) and an exceptionally aggressive approach at the plate (-0.56 c) with a league average likelihood to swing and miss (30% whiff/swing).
In summary, Belt has been excellent at discerning which fastballs and offspeed pitches are strikes and good at doing the same with breaking balls. All of this suggests a semi-young hitter who's going up to the plate with a sound idea of what he's doing.
Now that Belt has finally and perhaps belatedly been given a genuine opportunity in San Fran, don't be surprised if he settles in at an All-Star level over the next handful of seasons.