Both sarcastically and in earnest, there has been chatter about how the Mariners played so much better since Ichiro Suzuki was traded to the Yankees. They got off to a long winning streak shortly after the trade and many used that to draw an immediate causation. That talk has probably dropped as the Mariners have cooled off of late, but they are still 25-19 (.568) since the trade whereas they were 42-55 (.433) at the time. Meanwhile, the Yankees who were 57-38 have gone 22-23 since the deal.
For some, that's enough to confirm their preexisting beliefs. Ichiro always had his detractors for whatever reasons. But we're more thorough here. I cannot speak to any effect that Ichiro had or did not have in the Mariners clubhouse, but we can examine whether the Mariners' difference in won-loss record is meaningful.
It certainly seems clear that the Mariners have played better, but baseball isn't a single-team sport. That would be weird and yet very Seattle. Importantly though, the Mariners' more winning ways have coincided with a lot of games against bad teams. There were games against the Twins, the Royals, the Blue Jays and other such illustrious 2012 competition and the Mariners beat up on them. Using teams' current records (which isn't the best way, but it's what I have available), here's the average winning percentage of teams faced by the Mariners.
Before July 23: 0.521
July 23 - Today: 0.500
The difference between those two was a bit bigger before the weekend series against the Athletics, but it still shows the point well enough, the Mariners schedule got quite a bit easier after the trade.
So it was all just the schedule then? Hold up there, Huck. That's a bold and simplistic statement. The numbers aren't ironclad. Looking at strength of schedules is a murky business. Teams change over time and just as I stated above that won-loss records aren't necessarily the final word for judging the Mariners' performance, it's similarly uncertain for judging the Mariners' opponents as well.
However, I think it's a decent estimate and this is more about offering a different, deeper, way of thinking about the past games. It will not be a conclusive indictment because there are too many simplifying assumptions in order to make it easy to compute, but it can still be illuminating. I try to have one of LL's focuses to be on not buying into unsupported narrative and a part of that is trying to find alternate and reasonable explanations for why events might have occurred.
Assume for the time being that the Mariners were a .500 skilled team. That appears to be roughly the case as they're a little below .500 at the moment but also seem to have played a tougher than neutral schedule. Over the 97 games with Ichiro on the team, a .500 team playing an average of a .521 team would be expected to go 46-51. Instead the Mariners went just 42-55.
Over the 44 games post-Ichiro, a .500 team playing an average of a .500 team would be expected to go 1.000. Wait, no, they'd be expected to go .500, of course, 22-22. Well, the Mariners went 25-19 instead. Though the schedule was more difficult while Ichiro was here, the Mariners still did do worse than expected (again, assuming they're a .500 team) before the trade and better than expected after the trade.
Case more closed, right? Well, remember all the bits about how wins and losses aren't our best measurement for team performance? Runs scored and allowed are better and an interesting thing occurs when you substitute the Mariners' run numbers for their record. Instead of re-hashing it all with words, here's a chart.
As it turns out, the Mariners' run differential has tracked closely to their level of competition, and has the Mariners playing almost exactly to a .500 level.
Of course, some could still throw that on Ichiro's feet and say that the team underperformed in wins while Ichiro was here but now that they're free of his burndensome personality, they are able to soar to the heights of overachieving, like Angels. That's possible, sure, but a silly thing to just assume.
By the way, I mentioned in the last series preview that the schedule would get tough down the stretch. It's very tough. The newly completed series against the A's is just the beginning. The remaining 21 games are against teams that currently have an average of a .553 winning percentage.