Johan Santana's move from the Minnesota Twins to the New York Mets changed the power structure in the National League. Baseball Prospectus's PECOTA projection system—which considers, among other factors, past performance, age, height and weight—shows the trade knocking more than a third of a run off Santana's ERA: from 3.33 last year to 2.94. With Shea Stadium as his home park and a pitcher instead of a DH in opposing lineups, Santana's strikeouts could jump and his homers allowed could plummet. The Mets may have gotten the biggest impact player of the off-season, but other teams could get a lift as well from players who have changed addresses.
Dan Haren (right) is expected to boost an Arizona Diamondbacks' rotation led by ace Brandon Webb. Haren is coming off three 200-inning seasons for the Oakland A's. He peaked last year with the best rates for strikeouts (7.76 per nine innings pitched) and home runs (.97) of his career, as well as his lowest ERA (3.07). The move from spacious McAfee Coliseum to hitter-friendly Chase Field could have a negative effect on his home run rate and ERA, but Haren will give the Diamondbacks high-quality innings and make them the favorite in a competitive division.
The Detroit Tigers' new starting pitcher, Dontrelle Willis (left), saw his ERA nearly double (from 2.63 to 5.17) over the last two seasons with the Marlins. He gave up career highs in walks (87) and homers (29) in 2007, but he was playing for a team that had the worst defense in the NL as measured by Park-Adjusted Defensive Efficiency, a tool that evaluates a team's collective range. Partly due to that porous D, Willis gave up 241 hits. But now Willis will be pitching in front of a Tigers defense that was ninth in the majors in PADE and has upgraded defensively at shortstop with Edgar Renteria and in leftfield with Jacque Jones. If he merely pitches the same way he did in '07, Willis can still expect to see his hits allowed and ERA drop because of the improved defense behind him. If he nibbles less and goes after hitters more aggressively because of that defense, he could improve his walk rate as well. Willis may not have a season like he did in 2005, but he should be a good No. 2 starter for the Tigers this year.
For the Chicago White Sox, trading for Nick Swisher was an attempt to fill a hole in centerfield and boost a team OBP of .318, worst in the majors last season. Moving from a poor home run park in Oakland to a hitters' haven in Chicago is a bonus for Swisher, a fly ball hitter. Although he is merely an adequate defensive outfielder, his career OBP of .361 ranks behind only Jim Thome's among current Sox, and his .381 mark in '07 would have been second on the team. The Sox need base runners if they're going to challenge the Cleveland Indians and the Tigers, and Swisher addresses that glaring need.