It’s beginning to look like the Giants will make a strong push to re-sign left-handed reliever, Jeremy Affeldt. Per USA Today’s Bob Nightengale, the Giants are “confident” that they’ll be able to re-sign Affeldt for, what most are assuming, will be a three-year deal. Generally, when I hear about relievers getting multi-year deals, I grit my teeth a little. (The Dodgers, in a deal that may have already set the tone for the reliever market, have inked Brandon League to a three-year, $22.5M deal.)

The point of this blog post isn’t to point out that it’s silly to give free agent relievers lots of money and years (it usually is), but rather to point out the obvious: The Giants already have a pretty good Affeldt replacement on their roster — Jose Mijares.

Before we get too tied up in what Affeldt might get, let’s take a look at both relievers and how they stack up comparatively.

First, performance against left-handed batters.

It’s worth noting here that Affedlt — a veteran of 11 seasons — has pitched against LHBs more — 268 career innings to Mijares’ 107.1 career innings — when compared to Mijares. Affeldt certainly has the longer track record. That counts for something.

But, when comparing the two relievers’ work against LHBs, they’ve both been successful — though, they’ve done it in different ways. Affeldt’s bringing a pretty nice groundball rate against lefties to the table along with a little wildness (11-percent walk-rate). Mijares has thrown more strikes to lefties (6.6-percent walk-rate) and he’s posted a better strikeout percentage (23.6-percent) than Affeldt. In turn, Mijares’ FIP is more than a full run below Affeldts’. Mijares gives up more fly balls, but thankfully for him, AT&T Park limits the damage on most fly balls off lefty bats. Per StatCorner, AT&T’s HR Park Factor for lefties over the past three years: 86, 67, and 66.

Now, let’s look at their work against right-handed batters.

Ah, and here’s the biggest difference. While Affeldt has produced mediocre numbers against RHBs, Mijares has done quite poorly. Though, again, it’s worth mentioning that Mijares has thrown a total of 102.2 innings in his career against RHBs. You can’t pull much from 100 innings of work, but it’s probably safe to assume that Mijares’ lack of a third pitch hurts him against righties. Per FanGraphs’ PitchF/X data, Mijares occasionally throws a changeup, but it’s rare; he’s thrown just 162 of them since 2008. Though, the larger point stands; neither Affeldt or Mijares are particularly skilled at succeeding against RHBs. That’s an interesting point to consider because, over his career, Affeldt has faced twice the number of RHBs (2,354) than LHBs (1,146).

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So, in bidding for Affeldt’s serivices, the Giants are bidding for a reliever that’s done a good job of getting groundballs, but one that has trouble against RHBs. While I like Affeldt as an 7/8th inning reliever, it’s clear that he has his limitations – namely the fact that he doesn’t dominate LHB and he has some problems against RHB. As a team, the Giants place a huge premium on bullpen stability and it’s clear the team really values what Affeldt has done since he became a Giant. By the numbers, Affeldt’s 2012 was his best season as a reliever, which is pretty impressive since he started so poorly.

But, it’s hard to shake the fact that from 2010-2011, Affeldt was more of a replacement-level pitcher than a guy you want to spend $6-7M on per year. And, it’s hard to shake the fact that despite some differences in how they work, Mijares would be a pretty reasonable filler for Affeldt’s role. Even more so if Mijares can limit the damage that’s historically been done to him by RHB. I imagine that Dave Righetti will be working with Mijares this Spring Training on adding an additional pitch, or refining his changeup.

It’s hard to see how the market is going to play out right now. Will relievers get paid this year? Baseball appears to be flush with cash and as the League deal illustrates, it’s very possible that salaries will continue to go up. If the Giants feel comfortable with giving Affeldt a three-year deal in the $16-18M range, then they’ll go for it. And I think it’s pretty obvious that the Giants will attempt to bring back Affeldt. Everything Brian Sabean and the team has done over the past five years speaks to that. The Giants just love bullpen stability. Love, love, love it.

However, if not, look to Jose Mijares to fill in Affeldt’s bullpen slot — and at fraction of the cost. The results are likely to be very similar between the two.