It took 21 team games and 72 plate appearances, but Giancarlo Stanton finally hit his first home run of the the season this past weekend. He drove an 0-2 fastball from left-hander Mike Zagurski out to dead center field, a 425-foot three-run shot. It raised Stanton’s season line to .246/.288/.348 and was just his fifth extra-base hit, well below both projections and expectations. There are a number of reasons for the 22-year-old’s power outage in the early going, but the most obvious one is staring us right in the face: his new ballpark.

With some help from Hit Tracker Online, here’s a look at the new Marlins Park with an overlay of the Sun Life Stadium outfield dimensions…

Right away you can see how much bigger the new left field is compared to the old park, plus the straight-away center field wall is a little further away as well. Stanton has shown big time pull tendencies so far in his career, with a little more than three-quarters of his balls in play going out to left and center fields. Marlins Park has a 0.619 HR Park Factor according to ESPN, though we are obviously a very long way away from fully understanding how the new building plays with the roof open, with the roof closed, in midsummer heat and humidity, the whole nine.

Only 40 of Stanton’s 73 plate appearances this year have come at home (54.8%), so something else is going on here because he hasn’t been hitting the ball out of the park on the road either. Giancarlo has been playing through soreness in his left knee in 2012, dating back to Spring Training. There’s a chance he’ll have to deal with it all season according to Joe Capozzi of The Palm Beach Post. As big and strong as he is, Stanton still needs his legs — specifically his left (front) leg as a right-handed hitter — to transfer weight during his swing to generate that massive power. If the sore knee is compromising his lower half and creating what amounts to a weak link in the chain, his power will inevitably suffer. To what extent? We don’t know the answer to that, exactly.

Through the magic of Texas Leaguers, we can take a look at Stanton’s spray chart to see where exactly he’s been hitting the ball this season…

The points on the chart are where the ball was fielded by the defender, not necessarily where it landed. Including the homer, I count just six balls hit within shouting distance of the warning track by Stanton this year. That’s out of 53 total balls in play. We’re talking about a guy who came into the season with a career 24.0% HR/FB, and now barely more than 10% of his balls in play are threatening the warning track (6.3% HR/FB this year).

Stanton’s ground ball (49.1%) and fly ball (30.2%) rates are well off his career norms (44.4 GB% and 39.3 FB% from 2010-2011) early this season, which certainly makes sense given the lack of power he’s shown. The knee could be forcing him to hit the ball into the ground more than usual, it could be a mechanical/swing issue, or it could be dumb luck at this point. The good news is that his plate discipline stats are relatively unchanged, so he hasn’t altered his approach in an effort to hit more homers as of yet.

The calendar has just flipped to May and it’s still a little early to freak out about underwhelming performances. In Stanton’s case though, there is some tangible evidence that suggests his power outage is something more than just an ill-timed slump or the regular ebbs and flows of the season. His new ballpark is a factor but at this point it’s unclear just how much. I’m more concerned about the left knee problem right now, especially since there’s a chance it will linger all summer long. The absolute last thing you want to see such a great young player do is fight a nagging injury and a) hurt himself even more, and/or b) compensate for the injury in other ways and throw a wrench into what make him so successful in the first place.