The Numbers: Mike Pelfrey among first half's most improved

Each week, Big League Stew stat doctor Alex Remington will bring you a few baseball numbers you need to know.

The difference between Mike Pelfrey's(notes) career ERA before 2010 (4.58) and his ERA this year (2.69). Armed with his trademark sinker and a new splitter, the Mets pitcher has quietly transformed himself into one of the top starters in the league, even though his 5.9 K/9 and 1.79 K/BB are hardly elite.

Can he keep it up? Well, he had a tough outing against the Yankees on Saturday after going 5-0 over a stretch of six straight quality starts. He's also been getting lucky with men on base; his left-on-base (LOB) percentage is 80.7, well above the major league average of 71.7 percent. His ERA will rise, once more of these runners find a way home — perhaps even above Johan Santana, who's currently sitting at 3.31 — but he'll still almost certainly wind up with the best season of his career so far.

Marlon Byrd's major league-leading doubles total, which ties him with slumping Phillie Jayson Werth, who has just five extra-base hits this month. Like so many others before him, Byrd was a journeyman who suddenly found his batting stroke in his late 20s with the Texas Rangers. But now that he's at Wrigley Field, he may be headed for his best season ever. Byrd obviously has a decent bat, and the streaky Cubs will need him to provide them some consistency. To do so, he'll have to improve his walk rate as he's only walking in 3.6 percent of his plate appearances, far below both his career rate (6.9 percent) and the major league average this year (8.6 percent).

The Arizona Diamondbacks' NL-leading extra-base hit total. Unfortunately, they also lead the majors in total bases and runs allowed. They have a formidable offense, but one of the worst pitching staffs in the game: They've given up 405 runs in 70 games, an average of 5.79 a game. No other team has given up more than 379. It's little wonder they're in last place and one of the worst teams in baseball. They have some reason to hope from the pitching side — Dan Haren and Edwin Jackson's struggles were quite unexpected, and both figure to improve in the second half — and they have enough hitters to hang with almost anyone if they can prevent their opponents from putting crooked numbers on the board.

It's a little hard to believe, but the team that has given up the fewest homers in all of baseball is ... the Colorado Rockies. Coors Field is still a good hitters park, with miles of real estate for line drives and dying quails to fall, but between the humidor and Ubaldo Jimenez — the current NL leader in WAR, with 4.4 — it's no longer a home run-happy park. The Rockies are struggling to keep their heads above water in the surprising NL West, where the Padres rule the roost and the pitching-heavy Giants and hitter-heavy Dodgers are close behind. But they're playing on their terms. The Blake Street Bombers are long gone. Long live the Colorado Rockies' pitching staff.

The number of consecutive starts in which Stephen Strasburg has struck out at least eight men. He struck out 32 in his first three starts in the majors, an all-time record. It's also the first time anyone has started his career with three straight eight-plus strikeout games. The all-time record for most consecutive games with at least eight strikeouts is held by Randy Johnson — Johnson had 17 straight from September 24, 1999 to June 19, 2000, and 335 overall. Strasburg has quite an arm... but the Nationals' phenom still has a way to go.

The Boston Red Sox's team OPS with runners on base, well above their overall OPS of .821 (the best in baseball by 20 points) and even further above the next-best team with runners on, the Angels, whose OPS in such situations is .811. The Red Sox and Tampa Bay Rays are currently tied for second in the AL East, a game behind the division-leading Yankees, and it's sure to be a dogfight all season long. But the Red Sox — who were selling their defense hard all offseason — may actually have the finest offense of the three.

Cliff Lee's major league-lowest WHIP. Even more impressive is Lee's inconceivable 67/4 K/BB ratio, which would be by far the best in history if he can keep issuing one walk for every 16.75 strikeouts for an entire season. The current record is Bret Saberhagen's 11.0 in the strike-shortened 1994 season, set in just 24 starts.

Because he was injured to start the season, Lee has only made 10 starts so far. The Mariners have had a disappointing season, as their offense has been simply horrid, but Lee has been a radiantly bright spot, and figures to be the subject of a second straight deadline deal.