Umm, bring in one of the other 11-12 pitchers geared to go 2-4 innings on any given day? So you have 12 guys all capable of 2-4 inning outings and need 2-3 days off in between. For simplicity, let's say the 2 prior days went perfectly and you used 6 pitchers for 3 innings each. Now your guy gets shelled in the first inning and needs to get pulled, you now only have 5 pitchers to choose from as the other 7 are completely unavailable. And you actually only have 3 EXTRA pitchers to choose from as 2 are already earmarked for the current game. And again, this assumes everything works perfectly the 2 days prior. So your comment above makes no sense, because you will almost never have 11 pitchers available to pick from on a given day...only on opening day/after the all star break. Bad outings and extra innings would absolutely destroy this pitching strategy. It is not sustainable over the course of the season and won't ever happen. MLB is also actively making this strategy more difficult by soon limiting numbers of pitchers on the active roster, September callups, and changing the IL to 15 day instead of 10...making shuttle service strategy more difficult.