Here are the owners of the four lowest ERAs in the major leagues: Paul Maholm, Jake Westbrook, Clay Buchholz, and Carlos Villanueva. Obviously, they are going to give up runs at rate higher than that in which they have done so to this point. But which ones are going to do so at a rate acceptable enough to continue to roster them? And which ones are going to give up too many runs to keep?

Paul Maholm | Atlanta Braves | 100% owned | ERA: 0.00

This is a guy you should hold on to. He has had ERAs of 3.66 and 3.67 in the last two years and has seen his underlying skills improve. His strikeout rate increased last year and is up even more so far this year. Likewise, his walk rate improved and has continued to do so this season.

The improvement is likely the result of a shift in his approach. Prior to his emergence as a sub-4.00 ERA pitcher, Maholm was trying to be a heavy sinkerball pitcher. He threw that pitch 42% of the time in 2010. But since then he has used his slider more often (the pitch he gets the most whiffs with), he has added a cutter, and he’s getting more vertical break on his curveball. So the change in results is backed up by a change in what he is putting into the equation. He’s for real, and he should stay on your roster.

Jake Westbrook | St. Louis Cardinals | 24.1% owned | ERA: 0.00*

There is an asterisk next to Westbrook’s ERA because he actually gave up four runs to the Phillies on Tuesday, but the game was cancelled due to rain after just two innings. Right off the bat, you should know that Westbrook has not pitched as well as his ERA would indicate.

But the signs of bad pitching don’t end there. Westbrook has walked more than twice as many batters as he has struck out (10 walks, 4 strikeouts). His BABIP is low, his strand rate is high, and his SIERA is near 6.00. He checks all the boxes of regression. If somebody will take him, trade him for literally anything you can get. If no one will bite the proverbial hook, do not trot him out there against the Phillies again on Sunday. Leave him on your bench but still hope his luck continues so that his trade value continues to rise.

Clay Buchholz | Boston Red Sox | 100% owned | ERA: 0.41

Full disclosure: I’ve never been a fan of Buchholz, but with good reason, I believe. As far as I can tell, all of Buchholz’s success has been derived from pure good luck. In his breakout season in 2010 when he had an ERA of 2.33, Buchholz benefitted from the holy trinity of luck: low BABIP, high strand rate, few home runs. The next year the home run rate normalized and his ERA rose by a full run. But because it was still more than adequate in the mid-threes, no one paid much attention. But the next year, the BABIP normalized as well and he actually got bad luck with the strand rate and his ERA was an ugly 4.56.

The reason I say all the success was the result of luck is because he didn’t display much skill. You could say he wasn’t so much lucky with home runs in 2010 as he was good at preventing them. But given the fact that his home run rate from that year looks nothing like his home run rate from any other year, I’m going to chalk that up to luck. He does induce ground balls at a good clip, but that’s the extent of his above average skills. His strikeout and walk rates have both been consistently below average.

He has struck out batters at a good pace so far this season, but he’s not getting more swing and misses, so don’t expect that to continue. And his walk rate has actually been worse than it has been in years past. Regression is coming, and I recommend you trade him away. Don’t get greedy either. Take a player that you can be fairly certain about what you’ll get from him, and avoid the impending regression Buchholz will experience.

Carlos Villanueva | Chicago Cubs | 7.9% owned | ERA: 0.64

If I was ranking these pitchers for the rest of the season, I’d have them Maholm, Villanueva, Buchholz and Westbrook. Now, I obviously don’t think much of Buchholz, and I’d have Villanueva closer to Buchholz than I would Maholm. But given that Villanueva was essentially completely unowned last week and is still available in more than 90% of leagues, I think he’s undervalued at the moment.

In his last 31 starts (with the two from this year included), Villanueva has an ERA just under 4.00 (3.91). In those 31 starts he’s faced just over 1,000 batters and has a strikeout rate that is at or slightly above league average (19.4%) and an average walk rate of 7.9%. Those skills will play. They have led to an xFIP which is essentially 4.00 over the time frame of which we’re speaking.

This is what Villanueva is; he is a high-threes ERA pitcher with average-to-good strikeout and walk skills. His flaw is home runs. He’s allowed 35 in those 31 starts (1.29 HR/9). He plays in a park that gives up quite a few homers, so you should be able to navigate Villanueva’s starts to find the good ones. When he starts on the road, he’s worth a look so long as the matchup isn’t terrible. He gets Texas at home tomorrow (sit), at Cincinnati early next week (sit, also a bad HR park), and at Miami late next week (definite start). Assuming he gets roughed up a bit in his next couple of starts, he should be widely available for streaming in that Miami start.