What are the membership requirements for the Baseball Writers
Association of America, and how does one go about joining it?

Hello.

You have to be a reporter, editor, or columnist who covers baseball.
You can't work for an internet-only outlet.  You join after being
nominated by an existing member and then being evaluated by the
membership committee.

"The BBWAA consists of 825 reporters, sports editors, columnists and
feature reporters who cover baseball. Notably, journalists who work
for Internet-only outlets are not permitted to be members. Existing
members who have been with the BBWAA for at least 10 years may retain
membership cards and Hall of Fame voting privileges if they leave
their newspapers, but are still subject to regulations concerning
their type of news outlets.
New members may only be nominated by existing members. The nominees
are then evaluated by a membership committee, which meets twice a
year."
source: everything2.com
http://www.everything2.com/index.pl?node_id=1376925

search strategy:
"baseball writers association of america"

I hope this helps.

Thank you.