First, let's discuss what exactly happened yesterday. Bay and the Mets mutually agreed to make him an unrestricted free agent. Bay will receive the entire $21 million he is owed over a number of years. This is different from him being released, which would allow other teams to sign him for the league minimum while the Mets footed the rest of the bill for his contract. This way, Bay is free to sign whatever length contract he likes. There is no longer a $3 million buyout due at the end of this season, it is included in the $21 million mentioned above. Bay does not need to go through waivers and he is free to sign with whomever he pleases.
Who is he?
In short, a shell of his former self. Bay's three-year Mets career was awful. He hit .234/.318/.369 with 26 home runs in 1125 plate appearances. Last season, he hit a miserable .165/.237/.299 with just 8 home runs in 70 games. His BABIP was just .185, but awful is awful. This was a swift and severe fall from excellence for Bay, who hit 36 home runs and had 119 RBIs in 2009, his only full season with the Boston Red Sox.
Why should we care?
Because sometimes you can't help but hope that a player like Bay who fell off for no reason will return to his prior form. Bay had a .329 BABIP and walked in 11.0% of his plate appearances in 2010, his first season with the Mets. Even last season, Bay walked in 8.8% of his plate appearances, though a 27.7% strikeout rate didn't help things. There are still signs of a legitimate bat though. Bay hit .300/.418/.500 against left-handed pitching in 2011 and the walk rates speak for themselves. He swung at a higher rate of pitches outside the strike zone in 2010 and 2011, but his plate discipline returned to career form in 2012.
Why should we stay away?
Because he was cut by the freaking Mets, of all teams.
On a more serious note, there are some legitimate concerns following Bay. He's 34 years old and not getting any younger. His glove has always been horrible. If his power isn't completely gone yet, it will be soon. He was almost as bad as Ryan Raburn last season. His line drive rate dropped below 16% for the first time since 2006 and, as mentioned before, his strikeout rate last season was a ridiculous 27%. I'd add more, but it's hard to narrow it down from basically everything he did in the past three years. Plus, I don't want to ruin everyone's fun in the comments.
Will he end up in Detroit?
I highly doubt it. If he's signed to anything more than a one-year contract riddled with incentives, the Tigers overpaid. At this point, Bay is Jonny Gomes with a higher ceiling and a lower floor. Look for someone desperate for a power bat to sign him as a platoon outfielder or designated hitter.