Letter of the law, it is the correct call. However, one can argue that Middlebrooks had made a play on the ball and was in the position he was because of it. His intention to get up and continue the play is a direct result of the play on the ball. If that is the case, obstruction can be waived if my understanding of the rule is correct.
Let's not forget the Sox were in that position because of a number of 50/50 managerial and player calls earlier in the game. I like Farrell and his explanation of why Workman went to the plate made sense but in hindsight, he should have let Napoli bat. However, he can't manage in hindsight. Similarly, Salty shouldn't have thrown that ball, he struggles making routine throws to 2nd. There were other plays last night too that put them in that position. In the end, the series is only 2-1 and this Sox team is nothing if not resilient. Let's see what tonight brings.