Outside the box: MLB sees spike in extra innings

• Nearly 11%25 of all MLB games have gone into extra innings
• There is a strong inverse correlation between this percentage and the overall run environment

Each week, HighHeatStats.com will focus on one advanced statistic or trend. This week: extra-inning games:

Through July 4, 135 of 1,269 major league games (10.6%) had been tied at the end of nine innings. If this rate holds, it would be the highest percentage of games going to extra innings since 1965.

There is a strong inverse correlation between this percentage and the overall run environment. In 1999, when teams averaged 5.08 runs a game, 7.9% of games went to extra innings. This makes sense, as a higher scoring environment means that teams are more likely to score six, seven or more runs, and games are less likely to be tied at the end of nine innings. Comparatively, in 1943, teams averaged 3.91 runs a game and 13.8% of contests went to extra innings. When scoring is so low, each team is more likely to score a relatively low number of runs and games are more likely to be tied.

In 2013, teams are averaging 4.24 runs a game. The four most similar seasons, scoring-wise, were 1973, 1975, 1984 and 1990. Over those seasons, run scoring averaged the same 4.24 runs a game, but only 9.7% of those games went to extra innings, as opposed to 10.6% so far this year.

The increase in games going to extras is likely because of the style of game played today. Home runs are more prevalent in 2013 as compared with the four other seasons of most similar scoring, meaning that runs will tend to be scored in bunches. This makes it a bit easier for teams to tie games even when down two or three runs in the ninth inning. On the other hand, managers are less likely to call for a sacrifice or stolen base, and teams have become less capable of pushing across a tiebreaking single run late in a game.

Consequently, because of both factors, games tied in the ninth inning are more likely to advance to extra innings than they used to be.

Andrew Kamholz writes for the HighHeatStats.com, an affiliate of USA TODAY Sports Digital Properties.