After referee Gene Steratore used a decidedly low-tech tool to determine whether the Cowboys gained a crucial first down on Sunday night, there’s been more talk that the NFL needs a high-tech system to figure out whether the ball crosses the line to gain or goal line. Some have suggested taking a cue from tennis, which has a fast and simple replay method for determining whether a ball was inside, on or outside a line. There’s just one problem: The replay system in tennis wouldn’t work in the NFL. A spokesman for Hawk-Eye, the company with the patented tennis replay technology, told ESPN in 2015 that its system would be useless in the NFL. The Hawk-Eye system requires a camera that has an unobstructed view of at least 25 percent of the ball. In tennis, that’s easy to do. In football, with 22 players on the field, that’s often impossible: Plays like Dak Prescott‘s quarterback sneak on Sunday night occur with a dozen or more players blocking every possible camera angle.