Biggest sporting rivalry in your region?

[Tiger08]

Clemson vs South Carolina football

[100% pro-life no matter what]

Tennessee fans would claim it's "The Third Saturday in October" (Tennessee-Alabama), but rational people know that that's no rivalry (or a one-sided one).  Likewise, I'd say Vanderbilt-Tennessee, but that's also really a rivalry that only goes in one direction.  Middle Tennessee also has so many SEC fans of non-Tennessee based teams that the Iron Bowl could also be a plausible option.

For pro sports, it's probably Titans-Colts, though Titans-Jags and Predators-Blackhawks get a good amount of attention too.  Braves-Cardinals gets some attention (except for the fact that they aren't in the same division) because we kind of sit at the intersection of the fanbases (probably leaning a bit towards the Braves) and since they've been good at the same time before.

[Battista Minola 1616]

I am trying to do this again but excluding football (soccer), just for curiosity. It is interesting because really men's football is the be all, end all of team sports in Italy.

So, outside of football the biggest rivalry here in Liguria may be something in waterpolo, except that lately Pro Recco steamrollers everyone else regularly, so there is not much competition.
After that, we have the mythical sport of roller hockey where Sarzana is in the top league. Just to the south of Liguria there are Forte dei Marmi and Viareggio and I am confident that the two have a brutal hockey rivalry but not sure if Sarzana is really passionate against either of the two.

[Ancestral Republican]

Yankees - Red Sox.

[bagelman]

Browns are so bad there are plenty of Steelers fan leaking into northeast Ohio, especially towards the Mahoning Valley. At my old job in Portage County there were a few.