The Dome Effect: Does an Open or Closed Roof Impact Home Run Totals at the Rogers Centre?

In the past few years, the Rogers Centre has developed a reputation around the Major League as a hitters’ ballpark. A bit of a bandbox; a home run haven, if you will.

It certainly hasn’t always been that way, but recently it seems like home run numbers have mysteriously and steadily increased within the confines of the Rogers Centre.

But is that reality, or is it just perception – has the Rogers Centre really evolved into one of the most hitter-friendly ballparks in all of baseball? And does an open or closed roof really have an effect on the number of home runs hit inside the Rogers Centre?

Last week, I was watching a feature on the MLB Network which looked at the 50 longest home runs of the 2013 season. Not surprisingly, nine of the Top 50 were hit at the Rogers Centre; the most of any ballpark in MLB.

I also noticed the longest home runs in particular seemed to be when the Rogers Centre roof was closed. So I decided to crunch the numbers and investigate. Keep in mind these are only using results from the 2013 season. With 81 home dates every year, that’s a lot of box scores to comb through.

First off, I decided to go into the longest home runs of the season hit at the Rogers Centre in 2013.  There were a fair share of tape measure shots in Toronto last year, many of them hit by the opposition, and most of them with the roof closed.

Of the 25 longest hit home runs at the Rogers Centre, 18 of them came with the roof closed and only seven of them came with the roof open. If we expand that to the top 50 longest home runs hit at the dome in 2013, 34 of 50 came with the lid closed.

For the most part, when players get a hold of one at the dome with the lid closed, they launch it well into the seats at the Rogers Centre. Next, we go into the home run number comparisons between the roof open and closed.

Of the 81 home games played in Toronto during the 2013 season, 41 of them had the roof closed and 39 of them with the roof open. With the lid closed, 113 home runs were hit compared to 101 with the roof open.

I was surprised to learn the difference between home runs with the roof closed and open was not incredibly out of balance. It ended up being 2.9 home runs per game with the roof open and 2.4 home runs per game with the roof closed.

There seems to be this perception that the baseball just flies out of the park at as astronomical rate when the Rogers Centre roof is closed, but in 2013 that wasn’t quite the case. With the roof closed, it worked out to being just one extra home run every other home game.

I think the reason why people jumped to that conclusion was because for the first two months of the season, the Rogers Centre roof is predominately closed. Factor in a full 81 game home schedule and the numbers basically even out over the course of the season.

From there, we go a little further down the rabbit hole and do the splits between home runs hit by the Blue Jays at the Rogers Centre versus home runs hit by visiting teams.

Quite surprisingly, the visiting teams in 2013 had the slight edge in the home run department; 119 home runs for the visitors as opposed to 95 for the Blue Jays.

That may be partially due to the fact that the Blue Jays pitching staff as a whole was awful in 2013; they gave up the second most home runs in all of baseball (195) and surrendered the most home runs at home of any team in the majors at 119.

R.A. Dickey himself was responsible for nearly 20% of all the home runs given up by the Blue Jays pitching staff at home in 2013. Dickey has stated his preference to pitch with the roof closed, and judging by the results below, it’s for a very good reason.

In eight starts with the Rogers Centre roof closed, R.A. Dickey gave up seven home runs total last season which was less than one per game. But in 10 starts with the roof open, he gave up a total of 16 home runs, which works out to 1.6 home runs per start.

As ridiculous as it would be to have the roof closed on a hot summer day, it’s almost imperative the Blue Jays keep the roof closed whenever R.A. Dickey is on the mound … regardless of the weather forecast.

Lastly and perhaps most interestingly, it’s the split of day games with the roof open compared to night games with the roof open.

39 home runs were hit during day games with the roof open (or 2.05 per game) versus 62 home runs hit during night games with the roof open (or 2.7 per game). That works out to 0.65 more home runs per game with the lid open at night.

This is also somewhat surprising because conventional wisdom leads us to believe that warmer temperatures during the day would make the ball travel further instead of cooler temperatures at night. However, the results here prove the exact opposite.

I fully admit a one year picture is a fairly small sample size in the 24 year history of the Rogers Centre, but it’s interesting to see how things played out over 81 home games in 2013.

The numbers here didn’t completely debunk the myth that home runs fly out of the Rogers Centre, but at the very least it was indicative home run rates aren’t nearly as high with the roof open.

The real take away from all of this was the discovery that open roof night games produce 32% more home runs than open roof day games. Who knew?

Image courtesy of Rounding Third . Data courtesy of ESPN Stats & Information Group and RetroSheet.