I'd say since you can use it either one or two handed in a fight it would have its own category, sort of a bastard sword of clubs with different stats depending on how you use it.
If we're going for the bastard sword of clubs idea..
"Baseball bat" 1d8(m), 1d6(s), Crit: x2, Type: Blgn
For sake of completeness throw in;
"A Baseball Bat is about 3* feet in length, making it too large to use in one hand without special training; thus, it is an martial weapon. A character can use a Baseball Bat two-handed as a simple weapon."
Reasoning:
Baseball Bat is to bastard sword, as club is to longsword, as greatclub is to greatsword.
As such, bastard sword is up 1 level of dmg, but basically a longsword, so in this case. Up 1 step from club (minus the throwing-ness) to 1d8, but otherwise a club.
Also reduced the proficiency requirements per bastard sword, since BS is martial (as longsword) when two-handed, so BB should be simple (as club) when two-handed.
Did I miss anything? Any objections?
* How long are baseball bats? I'm lazy and I think it varies, right? Number subject to change to reflect baseball bat length
I'd say since you can use it either one or two handed in a fight it would have its own category, sort of a bastard sword of clubs with different stats depending on how you use it.
"Baseball bat" 1d8(m), 1d6(s), Crit: x2, Type: Blgn
For sake of completeness throw in;
"A Baseball Bat is about 3* feet in length, making it too large to use in one hand without special training; thus, it is an martial weapon. A character can use a Baseball Bat two-handed as a simple weapon."
I'd say a baseball bat is a club. At 32oz & 42" in length a typical bat is about the same mass and length as a typical longsword.
And remember, people wield longswords 1 handed or 2 handed.
If someone broke into my house and I had a baseball bat, I could swing it in one hand. But I'll use two hands, because I'm probably not also carrying a shield.
It's a club. Like, that's basically exactly what a club is. The only thing that doesn't work is that Pathfinder provides no benefit for a sub-14-Str person using a one-handed weapon in two hands. You should get an extra point of damage, or a +1 to your attack roll, or something.