I'm not a huge sports fan but this is an interesting idea. Currently a lot of people watch and post to Twitter during games but unless you've assembled a very well curated list of people, the signal to noise is usually terrible. That's going to be a big issue with any large chat group as we see in crowded YT and Twitch live feeds. I think the key is to have features that let mods curate the feed in real-time to spotlight good posts out of the fire hose of typical crap. Probably should also have an upvoting system that auto-elevates better posts to featured status (with votes automatically meta-weighted by user reputation, viewing frequency, etc).
I only watch recorded TV via DVR where I can easily skip commercials. For example, in the case of the NFL team I follow, I start watching their games on the DVR an hour and 15 minutes after it starts. After skipping commercials, time outs and half-time, I catch up close to real-time right near the end. So for me, such a service wouldn't be usable unless it had a good replay feature with granular DVR-like skip-ahead controls so I could keep the feed in sync.
