The Sox have a problem at SP (Porcello plus the hole left by Rodriguez' injury, which now appears to be more serious than originally thought), 3b (Panda), and LF (Castillo).
I didn't mind the trade to acquire Porcello, given that Cespedes was likely gone anyway. But to give him that massive contract right away was foolish. Yes he performed well in the second half of last year but in some ways it was a bit of smoke and mirrors. His babip, line drive rate, and strike percentages were virtually identical to that from the first half of the season.
The Panda situation has been discussed already at length. As for Castillo, I think it makes sense to try to maximize that asset, especially given the dollars invested in him. He's under contract through 2020 at $11.8m, $11.8m, $11.8m, $11.8m, and $14.3m. That's not much money if he emerges as a legit starting LF. But he's not there yet. And their commitment to him is for a long time. If that money is going to be spent, I'd like for him to become the best baseball player he can be, and for now, I think it's apparent that he stays in AAA until he gets sorted out and improves to the point where he can be a real starter for the major league club. Sitting the bench in Boston will not help matters.
So ideally, aside from Rusney suddenly getting it, the plan should be for him to be in AAA. But what about LF then? Holt will be fine there, and a platoon of him and Young should serve well. Even though Holt has a reverse split, him versus righties is still better than Young versus righties.
Vs. RHP (2015)
Holt: .270/.333/.368/.701
Young: .182/.246/.339/.585
Vs. LHP (2015, Career)
Holt: .312/.394/.413/.807
Young: .327/.397/.575/.972
So a Holt/Young platoon would likely give the Sox about a .790 ops combined from LF, roughly speaking. That .790 ops would have put them 7th in all of baseball, so that would end up being a positive thing.
But Holt is so valuable as a swiss army knife that I wonder what happens against righties when Holt is covering for Bogaerts or Panda or Pedroia. Maybe that's when Shaw plays LF? Because we really do not want Young in there against RHP. But Shaw also has reverse splits (or he did in 2015), putting up an ops of .723 against righties, and .975 against lefties. Still, either way it's better than Young.
So, lineup vs. RHP
C - Swihart/Hanigan
1b - Hanley
2b - Pedroia
3b - Panda
SS - Bogaerts
LF - Holt/Shaw
CF - JBJ
RF - Betts
DH - Ortiz
Lineup vs. LHP
C - Swihart/Hanigan
1b - Hanley
2b - Pedroia
3b - Panda
SS - Bogaerts
LF - Young
CF - JBJ
RF - Betts
DH - Ortiz
Lineup vs. RHP when Holt is playing for someone else
C - Swihart/Hanigan
1b - Hanley
2b - Pedroia
3b - Holt
SS - Bogaerts
LF - Shaw
CF - JBJ
RF - Betts
DH - Ortiz
You could do a lot worse. Shaw's flexibility helps, though I really have no idea how he'd do in LF. I really wish they had come to this conclusion earlier, moved Castillo to AAA, and let Murphy have a shot at the LF job. He's not exactly Ted Williams, but he does have a career ops of .795 against righties and could play a passable LF.