Rookie pitchers come with a warning: Check the expiry date before buying. With arm, shoulder and elbow injuries on the rise, teams are being careful with the workloads they’re asking of their young arms and, in many cases, setting innings limits. Early this past week, the Astros sent Lance McCullers Jr., arguably their top young hurler, to triple-A where, presumably, all he’ll do is watch games from the dugout. Two weeks earlier, they did the same thing with another prime pitching prospect, Vincent Velasquez. Following his late-May callup, McCullers breezed through his first 13 starts with a 2.48 ERA and a strikeout per inning.