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How long can the Red Sox wait for Rusney Castillo to hit?

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Rusney Castillo has yet to prove himself at the major-league level. How long can the Red Sox give him before moving in a different direction?

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The Red Sox are coming off of an exciting offseason, as we all know, and have subsequently made plans to contend this year. Of course, the second portion of that statement describes every team in the American League. As is typically the case when we’re talking about this kind of extreme parity, every team in the league has some flaws. Boston is no exception to this. There are a few areas that could undo this Red Sox team, but arguably the biggest question mark lies in the outfield, specifically with Jackie Bradley and Rusney Castillo.

The latter in particular is a large potential question mark. Even if you don’t believe in Bradley’s second half last season — which you probably shouldn’t completely, but that’s another story for another day — he has an elite glove that plays up the middle. He can make up for subpar offense if it comes down to it. Castillo is also a fine defensive player, but he’s nowhere on Bradley’s level and will be playing in left field, putting a lot more pressure on his bat. As we all know, the bat has been a disappointment over his career, to the tune of a career 83 OPS+. So, the question becomes: if he continues to struggle, how long of a leash can the Red Sox give him before looking in a different direction?

The first thing to look at when pondering this question is what exactly the other options are. If we had asked even a week ago, the answer would’ve been a lot different. There was virtually no outfield depth, with Bryce Brentz or Brennan Boesch arguably being the fifth outfielder on the roster. Bringing in David Murphy changed that. If it came down to it, a Murphy/Chris Young platoon in left field could have the potential to be very productive. Neither are close to star-caliber players, but as platoon partners they could be reminiscent of Daniel Nava and Jonny Gomes.

With that being said, a few things need to happen to make that kind of pairing in left field even possible. First and foremost, Murphy still needs to be around after the start of the season. He has the ability to opt-out of his deal at the end of camp and, given his experience in this league, there’s a decent chance he can find another job if he can’t get one with the Red Sox. It’s certainly possible that the opportunity won’t be out there, but it’s more likely that Boston will have to open up a roster spot to keep Murphy around. Unfortunately, an injury appears to be the only way to do that at the moment.

Oakland Athletics v Los Angeles Angels of Anaheim Photo by Stephen Dunn/Getty Images

Well, say the team finds a way to keep Murphy around. Miracles happen, and all that. Even in that scenario, a Young/Murphy platoon has another obstacle to jump. Young already has a platoon partner in Bradley. Luckily, it’s a bit easier to see this one working itself out, particularly because Bradley has shown reverse splits in his short time in the majors. As long as he gets off to a decent start — maybe not a given — one can see Farrell giving him a bigger role to help plug up another hole.

So, there’s that. If Castillo struggles at the major-league level once again, there’s an outside shot the Red Sox have an in-house option to replace him in a Murphy/Young platoon. There’s no guarantee they’ll both be available to replace him, but there aren’t many other options unless you want to convert Brock Holt to a full-time left fielder, which seems to be a misuse of his skill set. Now, we need to decide how long Castillo needs to struggle before the team makes a change. Obviously, this involves relying on small samples, so rather than looking at overall numbers like OPS, there are a couple of trends to watch for as the season gets underway.

The first of which is Castillo’s plate discipline. There’s no denying that he has been hurt by a lack of walks over his career. For reference, he’s walked just under five percent of the time in his 329 career plate appearances. You can survive with a low walk-rate, of course, but that involves jumping on pitches in the strike zone. Castillo, on the other hand, has swung at a large number of pitches out of the strike zone. Last season, his O_Swing_RT was the 33rd highest in baseball out of the 300 players who saw at least 1000 pitches.

This brings us to his other big question mark, and arguably the most important one: his power. When the Red Sox signed Castillo a couple years back, they knew they were getting an aggressive hitter. According to scouting reports, he’d be able to make up for that with plenty of good contact. That hasn’t come to fruition at the major-league level, to say the least. Instead, Castillo has been a ground-ball machine over his short career. In fact, in 2015 only Christian Yelich had a higher ground ball rate with at least 250 plate appearances, per Baseball Prospectus’ batted ball data. Castillo also finished the year with the lowest line drive rate in all of baseball. In fact, his 14.9 percent line drive rate was 3.5 percentage points behind the next lowest rate, which coincidentally belonged the Jackie Bradley. Even during his good stretch last season in July and August, Castillo was still hitting ground balls around 60 percent of the time without a large number of line drives. If he wants to survive in this league, he’s going to need to figure out a way to square up those pitches and turn them into extra base hits.

So, we know the possible replacement isn’t a guarantee to be around, but it’s a potentially productive duo if it is. We also know what Castillo needs to improve. Now, it’s time to decide how long to give him. Unfortunately, there’s not scientific way to figure this out, and it becomes more about gut feel. If we get four weeks into the season and the left fielder is still combining a lack of walks with the highest ground ball rate in baseball, it’s time to start platooning. If, after giving Murphy the majority of plate appearances against lefties, Castillo is still struggling after a couple more weeks and Bradley looks all right, it’s time to start thinking about benching Castillo entirely.

Obviously, injuries can happen and mess things up, giving him more time than one may want to give him. The point is, if Castillo is still using his aggressive approach to produce all ground balls and no line drives six weeks into the season, the Red Sox need to move in a different direction regardless of his salary. This is especially true in what’s expected to be a hyper-competitive American League.