Adjusting the New Starters for Toronto

The Toronto Blue Jays will be rolling out three brand new starting pitchers in their rotation in 2013. I’m sure some have been curious about how the transition from the National League will affect R.A. Dickey, Josh Johnson and Mark Buehrle. I am too, so we’ll take a look at how pitchers generally change from the NL to the AL, but I was also curious how the Blue Jays’ team defence may impact them, so we’ll look at that as well.

Changing Leagues

The best reference for pitchers changing leagues is probably this 2008 piece by Derek Carty, which used 2004-2008 to give us a rough estimate. It’s likely that there is updated data available but I couldn’t find a quick-and-dirty set of numbers like this one, so let’s use it as a rough reference. Carty suggests the following key changes for pitchers moving from the NL to the AL:
*K/9 drops by 0.57
*BB/9 increases by 0.05
*HR/FB decreases .21%
*ERA increases by 0.41

If we apply these changes to Buehrle, Johnson and Dickey, we see the following:

I also included Bill James’ projections for the metrics used here, since his will include adjustments for things like aging curves and historical comparables and the like. (I should also note that generally K% and BB% are better to use than per-9-inning stats, but these are far easier to apply changes to.)

Anyway, the conclusion here is not at all surprising – the AL is a more difficult pitching environment than the NL.

Park Factors

The next thing we could look at is Park Factors, which take into account the ballpark-specific factors at play on pitchers. It’s difficult to just apply these, since we’d also have to take into account the park factors of everywhere that pitcher will now pitch. However, starters will start half their games or so at home, so we can look at some macro-level changes they might be in for.

The two Miami starters can, for whatever reason, expect to allow more home runs and walk fewer batters, with a negligible impact on their overall run environment. Dickey, however, is moving to a park that was a bit tougher on pitchers overall.

Team Defence

The biggest area I wanted to focus on was, of course, the most difficult one to quantify. This is partly because run environments vary even within a team (that article focuses on both sides of the ball) and partly because defense isn’t terribly consistent year to year, at least with the current metrics available to us. Add in the fact that the Jays have a few new pieces rather than the same fielders as last year, and things get muddled even further. But let’s try.

My Beyond the Boxscore colleague James Gentile had an excellent article on adding defensive adjustments to ERA+ which gets to the core of the fact that even a factor-adjusted stat like ERA+ can’t account fully for the defence a pitcher receives. James proposed a metric called "xRA9+" which I won’t go into, but basically it gets into the guts of Baseball Reference’s calculations to strip out defense and adjust a pitcher’s ERA+ accordingly.

James was kind enough to send me his information on the Jays’ starters so we could try to evaluate.

Finally, we get some positive news here. It appears that all three of the new pitchers were subject to some poor defence in prior years (the higher the ERA+/xRA9+ the better, where "115" means 15% above average and "91" means 9% below average). In addition, we see that Morrow and Romero got slight bumps from the Toronto defence. Thus, you could expect a significant bump from the defence for the newcomers, moving from poor defensive teams to a good one.

It’s important to remember, though, that these changes aren’t always uniform across pitchers on a single team (in theory, Morrow and Romero could have gotten a bump while other Jays’ starters took a huge hit, but the Jays were a decent defensive team so in this case it’s probably legitimate).

One final thing we could check are the Jays’ additions defensively.

Things don’t look as friendly here, if you like DRS as a stat (I tend to find it holds up better than UZR/150 with what I see personally, but this is a very biased way of evaluating a stat). Izturis, Bonifaco and Cabrera aren’t major issues, but it appears the change from Escobar to Reyes could have a major impact on the team’s defence. UZR/150 actually backs up this finding as well, so it appears that, at least to some degree, part of the benefit for the new pitchers switching to Toronto’s defence behind them will be negated by Reyes.

What to Expect

It’s still far too early to tell, of course. Will Buehrle be able to hold up yet again? Will Josh Johnson return to dominance? Can Dickey’s knuckleball flutter at Rogers Centre? All of these are questions we won’t know for a bit.

But we do know that the change to the American League is somewhat unfriendly, the Rogers Centre is, at best, neutral with their previous parks, and part of the gains made from playing for a stronger defensive team may be negated by a defensive downgrade at shortstop.

I’m not trying to rain on anyone’s parade, though, because even a slight downgrade for this trio would give the Blue Jays a much improved rotation in 2013.

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