For a guy who didn't even make the majors out of Spring Training, Jonny Venters sure had a busy—and successful—rookie season. A rookie pitching in 79 games is impressive enough, but doing it despite spending the first two weeks in AAA is even more remarkable. Venters is left-handed, but he wasn’t used as a situational lefty. He actually pitched 83 innings in all (3rd most by a reliever in MLB), and went more than an inning 16 times.
Somehow, Venters' arm did not fall off from that extreme workload, though his performance definitely tailed off at the end of the year. He gave up as many runs in September (& October) as he gave up in April, May, June, and July combined. Perhaps Fredi Gonzalez will use Venters a bit less often in 2011 so that his arm stays fresh for the entire season.
Despite his September slump, Venters’ ERA never rose above 2; he finished the year at 1.95. That is the 13th-best debut ERA for a reliever (minimum 60 IP). Only one lefty ranks ahead of Venters on that list (the immortal Don "Ears" Mossi, otherwise known as the ugliest man to ever play baseball).
Venters' ERA is somewhat misleading, however, because he gave up a huge number of unearned runs. In all, Venters gave up 30 runs; 12 of those were unearned. To put that in perspective, that's more unearned runs allowed than Tim Hudson, Derek Lowe, Jair Jurrjens, and Kris Medlen had combined. Venters’ 12 unearned runs made up 40% of his total runs; the league average is usually around 8% of all runs. If those 30 runs were distributed more normally, Venters would have given up more like 28 earned runs (rather than 18). That would make his ERA over a run higher (3.04)—still good, but not dominant.
Based on this and on his FIP (2.69), I think it's unreasonable to expect Venters to match his 2010 ERA going forward. Of course, an ERA in the 3.00 range is nothing to sneeze at, especially when it comes from a durable lefty who gets lefties and righties out equally well (vs. RHB: .543 OPS, vs. LHB: .570 OPS).
Some have been advocating Venters for the closer's role in 2011. While that is not a bad idea, I think that Craig Kimbrel is a slightly better fit for a couple reasons. First, I think Kimbrel's strikeout potential is much higher. Second, I think Venters would be a great fit for a sort of "fireman" role, in which he would be brought in to face the heart of the opponent's lineup in crucial situations, regardless of the inning. Being able to get both lefties and righties out is a huge advantage in those sorts of situations. Venters’ ability to induce ground balls (68.4% groundball rate, 11 double plays) is also very helpful in the "fireman" role.
Regardless of what role he ends up with, Venters has established himself as a key component of the Braves’ bullpen for years to come. That's a pretty impressive feat for a guy that most Braves fans didn't know much about a year ago.