A legal battle over insurance claims may be the last thing to attract the attention of football fans still chewing over draft picks and just what Tom Brady did or didn’t do.

But with an estimated $1 billion at stake, it is front and center for the N.F.L. and its insurers, and it may say a lot about the league’s paramount health issue: what it knew about the debilitating effects of repeated head hits, and when it knew it.

The dispute is tied to the settlement between the league and the thousands of retired players who said the league hid from them the dangers of repeated head hits. Players stand to receive up to $5 million each.

But where exactly would that money come from?

Its insurers, the N.F.L. says. But the insurers, a group of about 30 companies, have gone to court to get out of paying.