The Mystery Of The Blue Jays Sudden Home Run Surge May Not Be So Mysterious After All

The Toronto Blue Jays are one of the biggest surprises in baseball this season with the second-best record in the American League, thanks in large part to an offense that is hitting tons of home runs in an era when home runs are down.

But what is curious about the Blue Jays is that the offensive increase in production has come with almost the same lineup as last year.

There have also been a lot of home runs like this one by Juan Francisco, an opposite field, line drive that did not look like a home run when the ball came off the bat.

But before everybody starts whispering "steroids!" there may actually be a simpler explanation.

The surge in offense by the Blue Jays may have little to do with the players and a lot to do with the ballpark they play in. The Rogers Centre may be juiced this season.

The Blue Jays are hitting a lot more home runs, but only at home

The Jays are on pace to hit 228 home runs this season, an increase of 23.2% over last season (185). That increase is almost entirely from home runs at home.

Toronto is on pace to hit 132 home runs at the Rogers Centre this season, up from 95 last year. Meanwhile, their hitters are only hitting marginally more home runs on the road this season.

It is not just the hitters

The increase in offensive production north of the border is not just impacting the hitters. The Blue Jays pitchers are suffering at home just as much as the hitters are succeeding.

In 2013, opposing hitters were slightly better in Toronto (.767 OPS) as opposed to when the Blue Jays were playing on the road (.733 OPS). This year, that difference has nearly tripled with opposing hitters posting an .800 OPS in the Rogers Centre.

It is not just the Blue Jays

The Rogers Centre suddenly turning into a hitter's paradise is most pronounced when we look at the ballpark factor which looks at how all hitters (Blue Jays hitters and visiting hitters) do when playing in Rogers Centre compared to how those same hitters do in other parks.

For the last ten years, Rogers Centre has been a neutral ballpark (100=average, does not favor hitters or pitchers). Suddenly, this season, the Blue Jays home park looks a lot more like Coors Field, a park with a strong reputation as the best park for hitters.

There are ways to make ballparks more hitter friendly

There are reasons why a ballpark factor might fluctuate from year-to-year without changing the physical structure of the stadium (e.g. moving the fences).

The biggest factor is weather, where something like an unseasonably warm spring could make a stadium more hitter friendly. But in the case of the Blue Jays, they play in a park with a retractable roof.

In fact, that roof may be the biggest factor. So far this season, the Jays have only opened the roof in 11.1% of the games, well down from 2012 and 2013.

A team playing indoors can also make slight adjustments to the air conditioning that could have a huge impact on how far baseballs travel.

There is no evidence that the Blue Jays have adjusted the air conditioning. But by keeping the roof shut it appears that the Blue Jays have transformed their ballpark into Coors Field East.

It is still early in the season. It will be interesting to see if the Jays start to open the roof more often when the weather warms up or if they stick with the closed roof which accentuates their strengths and makes them a better team.