Pitching this well with Yankees Stadium as your home park is going to get you attention from more than just your current team.
Brandon McCarthy has been nothing short of excellent in his 70+ innings since coming over in a trade from the Arizona Diamondbacks. Obviously, as far as this season is concerned, acquiring a pitcher for practically nothing and having him pitch to an ERA under three is nothing but a positive. And it's not some fluky or fortunate run of success: his FIP is under three as well, and he's already fifth on the team in pitching fWAR despite having only joined the team in July. Another positive is that McCarthy has said that he likes playing for the Yankees and would be open to a return engagement. That's all well and good, but McCarthy's success is putting him among the best free agent options for teams in need of pitching in 2015.
The free agent class is obviously headed by frontline talent like Max Scherzer, Jon Lester and James Shields. But not everybody is going to be in the market for a Ferrari, and even those that are might need another quality car in addition to that. For those not looking to have to give a pitcher a deal that goes for five years or more there's a couple of options, but I think McCarthy profiles as well or better than most of them. Jake Peavy has had similar success after his being traded, but he's a few years older and doing his good work in the National League. Jason Hammel has overcome his hiccups initially with the Oakland Athletics to get back to pitching decently, but his FIP for the season is now over four. Francisco Liriano, and Ervin Santana can all count themselves amongst that "second tier" of pitchers available in 2015.
Problem is I don't think any of those options are more appealing to a team than McCarthy. Forward-thinking front offices are very likely going to look at McCarthy's struggles in Arizona as more of an aberration than an indication of him being a risky proposition. A fastball that consistently sits at 93 miles an hour with plus command and a nasty cutter? Even less statistical-savvy teams would want a pitcher with a profile like that.
I would suspect the biggest competition will come from the Boston Red Sox. A conservative estimate is that the Red Sox will need to acquire three pitchers in the offseason if they want to make a run at the division title next year. Acquiring McCarthy and proving that his stuff can play in the AL East only to lose him in the end to a hated rival would be a difficult pill to swallow. But it can't be helped when a player raises his stock with your team as much as McCarthy has.
In the end, the Yankees will be a team desperately in need of hitting that will be able to add the most talent by signing pitchers. When the patchwork pitching staff has been this good that might seem like an illogical allocation of funds, but you can't force the market fit your needs. Ideally Brandon McCarthy will be a part of their spending spree, but if his demands start getting into a fourth year bringing back a good pitcher and his delightful wife might be less than sound. Regardless, it's been a hell of a third of a season he's put forth.