I've already introduced Nook "the Crook" Logan because of his propensity to steal bases (he's a good law-abiding citizen, hereafter glac).
There's rookie pitcher Joel "Sirhan Sirhan" Hanrahan because he's a killer at RFK (or hopefully he will be).
Those are the best that I've come up with.
I prefer "Z" as Ryan Zimmerman's nickname over "Zim." It's easier to yell.
Shawn "King of the" Hill is fairly obvious. Hopefully he'll be back soon healthy and pitching like he did earlier in the year.
You've got Ryan "take 'em to" Church or Ryan "Amen" Church, whichever's better.
Ronnie "Ring my" Belliard is a not very good pun based on a popular disco song.
I have a policy that I don't call players on my favorite team by their first names until they've played at least a year on the team, except in special cases, like Ronnie and Dmitri.
Manager Manny Acta has done a great job this season.
He has no nickname yet.