Bay Inks with Mets

According to MLB.com’s Bill Ladson, free agent OF Jason Bay has come to terms on a four-year, $66 million deal with the New York Mets, pending a physical. Bay’s contract reportedly includes a vesting option for 2014, too.

Bay, 31, was actually Mets property back in 2002. The former Gonzaga star was a 22nd round pick of the Expos in 2000. He was dealt to the Mets in March of 2002, only to be traded to the Padres in July of ’02 and then the Pirates in August of 2003. The Bucs shipped Bay to the Red Sox as part of a three-team deal in July of 2008.

The 6-2 righty batter can mash, but his defensive shortcomings do dent his value. Bay has a career -8 UZR/150 in left field, and his recent work has been even less appealing.

There’s a lot to like about the bat, though. Bay has a career 137 wRC+, meaning his offensive production has been 37 percent above average once we account for park and league factors. He suffered a down 2007 season (97 wRC+) as he battled a knee injury, but Bay bashed to the tune of a 138 wRC+ in 2008 and a 142 wRC+ in 2009.

A highly disciplined hitter, Bay has walked nearly 13% of the time during his big league career, with a 19.4 outside swing percentage (the MLB average has been around 25 percent in recent years, though it was lower in 2004 and 2005).

His career ISO is .240, and checked in at .269 in 2009. Bay isn’t a big stolen base threat, but he snatched 13 bags in 16 attempts this past year. The Canadian has crushed fastballs (+1.70 runs/100 pitches), with positive run values against changeups (+0.46) and sliders (+0.42) as well. Curves haven’t been his kryptonite, but he’s at -0.21 runs per 100 tosses against the pitch.

How will Bay fare in Citi Field? It’s hard to make any bold conclusions based on just one year of park data, but Citi did play like a pitcher’s park in its inaugural season. According to the Bill James 2010 Handbook, Citi Field depressed run scoring eight percent compared to a neutral ball park. Home run production was stunted by four percent. Lefties (93 HR park factor) felt the effects more than righties (99 HR park factor).

That’s not as hospitable as Fenway, which has increased run scoring by 11 percent compared to a neutral park from 2007-2009. Homers are hard to come by because of the Green Monster (91 HR park factor), but doubles are plentiful. Fenway has boosted two-baggers by 45 percent since 2007.

Baseball-Reference’s Play Index Tool gives the option of taking a batter’s line and adjusting it, based on the offensive level of the league (NL or AL) and the run scoring environment of the ball park. According to the Play Index Tool, here’s what Bay’s 2009 season would have looked like, had it occurred in Citi Field:

Actual: .267/.384/.537, .269 ISO
Adjusted: .265/.380/.535, .270 ISO

The net impact doesn’t appear to be huge. On one hand, Bay is going from a clear hitter’s venue to a park that played as pitcher-friendly in 2009. But on the other, he’s moving back to the NL. Derek Carty of The Hardball Times showed last off-season that batters going from the AL to the NL receive a slight boost in contact rate, home run per fly ball percentage, singles and doubles.

Whether Bay is worth four years and $66M remains to be seen. But as for 2010, his move to Queens shouldn’t change his fantasy value tremendously. Luckily, you don’t have to worry about how a 34 or 35 year-old Bay will produce.