Why Do Astros Score More In Late Innings?

You probably have heard broadcasters say that the Astros' offense doesn't wake up until the 7th inning or later.  "Nobody has an explanation for why this is the case,"  say the television broadcasters.  I have even heard the suggestion that the Astros' hitters lack focus and intensity until the late innings.

Looking on this as a challenge: Is this true?  And, if it is, what is the possible explanation.  I will use Baseball-Reference.com's splits pages for the Astros and the American League to shed some light on these questions.

First, the claim that the Astros' offense is skewed toward the late innings is true.  You probably knew this from watching the Astros' games.  But the stats help us verify the claim.   The tables below show the percentage of runs scored by inning and the OPS+ by innings.

Percentage of Runs Scored
inning	AL Avg.	Astros
1 thru 3	36%	32%
4 thru 6	35%	28%
7 thru 9	29%	40%
	Splits- OPS+
inning	AL OPS+	Astros OPS+
1 thru 3	104	99
4 thru 6	94	83
7 thru 9	100	120

As shown above, the Astros' offense is skewed toward the late innings, particularly in comparison to the average AL team.

The "late and close" statistics are based on  7th inning or later  situations in which the game is tied or within 1 run or with the tying run in the on-deck circle.  Here the Astros are again significantly better than the AL average for late and close for t OPS+ and s OPS+.  [ NOTE:  t-OPS+ is the OPS relative to the team's own average and s-OPS+ is the OPS relative to the league for this situation. ]

	late and close
	AL Average	Astros
t OPS+	84	110
s OPS+	95	112

In addition the Astros' offense has performed significantly better than the AL average during high leverage situations.  Since leverage takes into account the inning, score, and runner on base situation, the results are similar to "late and close."

	High Leverage
	AL Average	Astros
t OPS+	97	116
s OPS+	98	116

This is impressive performance by the Astros in the most critical situations.  But this doesn't answer the second question: Why?

Substitutions

One factor is that the Astros' bench has performed well when they are inserted into the game as substitutes.  This typically happens in the 7th inning or later as starting pitchers leave the game, and the batting order is adjusted for the handedness of relievers.  The Astros have received more offensive jolt from substitutes than the average AL team, and this undoubtedly contributed to offensive performance in the 7th inning or later.

	Starters vs. Substitutes (s OPS+)
	AL Average	Astros
Starters	99	98
Substitutes	120	180

The favorable substitutions may reflect well on Manager A.J. Hinch's decision making.  However, the sample size here is small, and it seems improbable that the substitutions are the primary reason for the Astros' higher scoring in the late innings.

Astros Vs. Relief Pitchers

The 7th inning marks a point when starting pitchers are frequently replaced by relief pitchers.  The Astros have been significantly better at hitting relief pitchers than starters.  This is out of the norm, since AL teams typically have more difficulty against relief pitchers.  The s-OPS+ for hitting against starting pitchers and relief pitchers is shown in the table.

	Vs. Starters and  Relievers
	AL Average	Astros
starter	101	94
reliever	100	114

Notice that the Astros' and the average AL team's relative strength against starters and relievers is more or less reversed.  Russell Carleton at Baseball Prospectus demonstrates in this article that bullpen pitchers have grown in effectiveness at a higher rate than starting pitchers over the past decade.  As a result, some have questioned whether the tactic of trying to force the starter out with a high pitch count continues to be effective.  The average AL team hits starters better than relievers.  However, the Astros have found that their offense struggles against starting pitchers but is productive when the opposition's bullpen takes over.  Carleton suggests that teams should acquire or develop hitters who are particularly skilled at batting against pitchers with reliever-like qualities, such as high velocity.

I don't have a definitive answer as to why the Astros are more effective than other AL teams against relief pitchers.  But it's possible that the Astros' hitters match up better against relief pitchers.

Besides the velocity difference, starting pitchers tend to use more types of pitches than relievers.  A minor leaguer with only two pitches of major league quality usually will be channeled into the bullpen.  Perhaps the Astros' batters, overall  younger than the average team's batters, are more effective against the fastball oriented relief pitcher but struggle against starting pitchers with 3 or 4 pitches.

One approach to identifying the strengths and weaknesses of hitters is to analyze the frequency of various types of pitches thrown by opposing pitchers.  Opposing pitchers identify hitter's weaknesses more rapidly than a typical statistical analysis.

The table below, derived from Fangraphs' pitch f/x team data, shows the Astros' hitter ranking in pitch type frequency relative to the other 29 teams.   Presumably the opposing pitcher's relative usage of pitches tells us something about the "book" on Astros' hitters.  A higher ranking should indicate that the team is perceived by pitchers as weaker against that pitch type.

Team Batter Ranking: Pitch Frequency
		(team rank)
4 Seam FB		28
2 Seam FB		12
Sinker		18
Slider		18
Curve		21
Change up		9

The Astros' rank suggests that hitting fastballs is a strength of the Astros' batters, breaking pitches are a relative weakness, and that the Astros' batters are particularly susceptible to change ups.  Since many relievers rely more heavily on fastballs, perhaps this explains why the Astros have been more effective when they get into the opposition's bullpen. Starting pitchers are more likely than relievers to rely on change ups. If the Astros' batters are indeed susceptible to change ups, this may provide some explanation of their struggles against starting pitchers.

This isn't presented as a definitive explanation of the Astros' reliance on late inning offense, but it's a hypothesis which may be at least a partial explanation.