Wilson Sporting Goods put the number of Jack L. Frolow's tennis racket patent on 14 models of its tennis rackets. It also paid Frolow royalties on 299 racket models. Yet the district court granted Wilson summary judgment on the theory that Frolow hadn't put forward any evidence that the rackets infringed his patent.

The Federal Circuit reversed. It held that Frolow's evidence raised an issue of fact on the infringement question. Wilson's marking and payment of royalties provided circumstantial proof of infringement, the panel ruled, although perhaps not enough by itself to defeat summary judgment. But the court declined to treat Wilson's conduct as a species of estoppel. Frolow v. Wilson Sporting Goods Co., No. 12-1185 (Fed. Cir. Mar. 15, 2013)

Circuit Judge Newman concurred, urging that on remand Wilson should have to negate infringement by the 14 racket models.