Despite only being a back-up caliber catcher, Leon's cannon arm and above-average defensive skills behind the plate would have been picked up by a number of teams for free. This way, the Nationals will at least get some value for letting the Red Sox enjoy his services. Leon is a veteran of 34 games across 3 seasons with the Nationals, hitting only .189/.280/.253 in that time. He hasn't been much of an offensive force in the minors, either, outside of a 117 wRC+ run in 40 games at AA in 2012, followed by an incredible outburst of 188 wRC+ in 19 games at AAA which earned him his first call-up.
The projection system ZiPS projects Leon for a .217/.285/.317 batting line in about 300 plate appearances, which is worth about a 69 wRC+ or 31 percent below league average.. He's also projected to save about 13 runs on defense. in 83 games, making him overall worth about 12 runs above replacement level. While it's doubtful that the Red Sox would need to turn to Leon for that many games, he is a better option than veteran Humberto Quintero, who is decent on defense, but projected to be even worse on offense.. Quintero also isn't on the 40-man roster, meaning the Red Sox would have to make a move to put him on it. Top prospect Blake Swihart is on the 40-man roster, but the Sox would prefer to send him to AAA Pawtucket for further seasoning.
Leon should serve as a more than serviceable back-up to the Sox's other catcher, Ryan Hanigan, until Vazquez returns or Swihart proves he's ready for the big leagues. It's a good value pickup for the Sox in any case.