That may be happening in the case of Adidas and Reebok, if this article from the Portland Oregonian is a guide.
[In April] took over a licensed merchandise deal with the NBA from Reebok, acquired in January. Last week it started selling new fashion sneakers designed for each of the 30 NBA teams and has poured more money than ever into basketball marketing.
But perhaps Adidas' own Reebok, and not Nike, will be the biggest loser. Reebok, whose overall business is lagging in sales and order backlogs, has rapidly ceded market share in basketball.
Adidas' market share in basketball shoes has climbed, but so has Nike's. It's Reebok who has dropped.
"It's difficult enough to compete against everyone else, let alone having to compete against your brother," said Matt Powell, contributing editor for Sports Executive Weekly, an industry publication.