Should Jeff Bianchi take over the right half of the 2nd base platoon?

The answer: probably not, but it depends on how much you weigh Rickie's struggles to start the year versus his expected performance, and it's a bit closer than I had previously thought.

People are calling for the head of Rickie Weeks after he went 0-2 with a walk and continued to struggle in the field on Saturday night in the 8-7 win over Pittsburgh. He did not help his cause by striking out on 3 pitches against Gerrit Cole in a pinch-hit appearance on Sunday. Things have not looked good so far, but let's think through a few reasons why dumping Weeks at this point might be unwise:

• He has only 25 plate appearances so far. Weeks has been well off his peak 2007 to 2011 production for a while now and it's safe to say that's not coming back. However, it's a bit of a stretch to think he has completely lost it and can't still be the .230/.328/.400 hitter he was back in 2012.
• Scooter Gennett is not very good against lefties. For a team looking to contend, starting Gennett regularly against left-handers is not an option. This point brings us to point 3...
• Jeff Bianchi doesn't really hit much at all. The gains we would see from Bianchi are almost completely on the run prevention side of things.

It seems incredibly obvious to point this out, but the decision comes down to what we expect out of Rickie. Are we ready to revise the Weeks offensive projection significantly downward based on a 25 PA sample?

Weeks came up through the minors with a bad defensive reputation. Both major advanced defensive numbers, TotalZone and UZR, tell similar stories about Weeks-- he was very poor as a young player, improved and was around average in 2009-2011, and fell off significantly in 2012 and 2013. Bianchi is much tougher to get a read on statistically; evaluating his defense so far is something like trying to evaluate a hitter's skill based on about 100 plate appearances. What we do know is that all of his fielding numbers have been positive, he has a good defensive reputation, and watching him play gives you the idea that he is a very good fielder.

The rest is really guesswork. The Brewers have about 200-250 plate appearances left to fill with the right-handed side of the second base platoon. For the math I will use the rest-of-season ZiPS projections. Weeks has a significant career platoon split, hitting lefties much better than righties. Bianchi has not shown much of a split in the majors. That would normally call for an upward adjustment to the Weeks numbers, but given how little he has shown us so far I make the conservative assumption and will not apply an adjustment

Weeks: .233/.321/.399, works out to 2 runs above average in 250 PA

Bianchi: .239/.278/.320, comes to 9.6 runs below average in 250 PA

Because we are talking strictly about second base, if you buy those projections going forward, you would have to think that there are more than 12 runs separating the two in the defensive innings in the field they would accumulate while picking up those 250 plate appearances. That's certainly possible-- if we think Bianchi is a +10 defender in a full year, and Weeks is now a -10 defender, we are talking about something close to a wash.

The moral of the story is that right now there is not much to separate the projected performance of Weeks and Bianchi going forward. That is not enough for me to recommend making a change, considering that we have seen so much better out of Weeks in the past and his upside offensively is far greater. That doesn't even consider other points that management would consider a valid tiebreaker-- his importance to the franchise in the past decade, clubhouse dynamics, and his salary. It is not really fair to make a rash move on a player based on less than about 100 plate appearances. But if we get to that point in a month or so, and Weeks has shown no signs of life, it might be time to start thinking about making a change.