Last time, I showed that the opening day order of a starting rotation will rarely be in order of that season's performance level. This is due to several reasons, including injuries, veteran preference, matchup strategies in deploying the rotation, and surprises or disappointments that a player experiences. Of the 20 teams observed, though, nine opening day starters ended up being the team's best and four more ended up being the team's second-best starting pitcher. Chances are, if you are facing a team's opening day starter, you are facing one of their better pitchers.
Next, I wanted to take a look at the assumption that teams' rotations are actually aligned over the course of a season, allowing #1 starting pitchers to regularly face #1 starters and #4 starters to regularly face #4's. I did this by looking at the Tigers' 2007 opening day rotation and the starting pitchers that they faced in each of their starts. A Number 6 starter is defined as one who didn't start
Jeremy Bonderman (Opening Day Rotation: #1)
Faced #1: 5 times (20.8%)
Faced #2: 3 times (12.5%)
Faced #3: 2 times (8.3%)
Faced #4: 5 times (20.8%)
Faced #5: 3 times (12.5%)
Faced #6: 6 times (25.0%)
Average SNLVAR of opposing pitcher: 3.2625
Nate Robertson (Opening Day Rotation: #2)
Faced #1: 3 times (9.7%)
Faced #2: 3 times (9.7%)
Faced #3: 5 times (16.1%)
Faced #4: 4 times (12.9%)
Faced #5: 4 times (12.9%)
Faced #6: 12 times (38.7%)
Average SNLVAR of opposing pitcher: 2.3129
Justin Verlander (Opening Day Rotation: #3)
Faced #1: 8 times (25.0%)
Faced #2: 2 times (6.3%)
Faced #3: 6 times (18.8%)
Faced #4: 7 times (21.9%)
Faced #5 5 times (15.6%)
Faced #6: 4 times (12.5%)
Average SNLVAR of opposing pitchers: 3.0469
Mike Maroth (Opening Day Rotation: #4)
Faced #1: 4 times (30.8%)
Faced #2: 1 time (7.7%)
Faced #3: 1 time (30.8%)
Faced #4: 2 times (15.4%)
Faced #5: 2 times (15.4%)
Faced #6: 3 times (23.1%)
Average SNLVAR of opposing pitchers: 3.9615
Chad Durbin (Opening Day Rotation: #5)
Faced #1: 2 times (10.5%)
Faced #2: 3 times (15.8%)
Faced #3: 3 times (15.8%)
Faced #4: 2 times (10.5%)
Faced #5: 4 times (21.1%)
Faced #6: 3 times (15.8%)
Average SNLVAR of opposing pitchers: 2.4824
As this shows, it appears to be random as to which pitcher a starting pitcher will oppose. While Jeremy Bonderman faced #1 pitchers in 20.8% of his starts, Justin Verlander and Mike Maroth both faced the opposing team's ace more often in their starts. Nate Robertson, the #2 starter, faced easily the weakest starting pitchers of anybody over the course of the year.
Several aspects lead to the randomness of pitching matchups.
-Injuries: Justin Verlander is the only Tigers pitcher to spend the entire season in the rotation. Injuries in a rotation can cause a pitcher to be moved up a day, back a day, or inserted into the rotation at the most convenient spot. With how often pitchers miss starts, it's a wonder that anybody could begin to think #1's face #1's.
-Rotation Style: The role of the fifth starter varies by manager. Many skippers will go 1-5, while several will use their fifth starter only during streaks of five or more games without an off-day. Chad Durbin's first start was pushed back to the sixth game of the season, so the #5 starter was facing the Blue Jays' #2. Different managers deploy their starters in different ways, and it is impossible to say that pitchers will be aligned based on their opening day spot in the rotation.
-Weather: All it takes is one rain-out to move a rotation up or back a day. In the case of the Mariners and Indians last April, their rotation was reset after a snowy weekend off. Postponements lead to another rotation juggler: double-headers. Spot starters come up from the minors, possibly facing that day's starter. Overall, the weather can play a large role in rotations becoming out of sync.
-The All-Star Break: The most boring three days in the baseball season also help to throw this myth into disarray. Rotations are frequently reset after the all-star break. Some team's aces go the first game after the break, while some aces are given a few days to recover from their All Star appearance. I assumed that there may be a chance that an All Star pitcher would face more aces after the break, but Justin Verlander faced just three of his eight after the All Star Break.
-The Schedule: Some teams play six games in a week; some play seven. Once again, teams' rotations get out of sync.
If teams played one game every day in domes, and pitchers never ever got hurt, you could make the case that pitchers at the bottom of a rotation have an easier time. The problem is they don't, and as such, anybody who uses a pitcher's spot in the rotation as an excuse probably doesn't know what they are talking about.