The San Francisco 49ers gave up a touchdown pass to Brandin Cooks, and as the GIF above shows, Cooks blew past Jimmie Ward. What is tough to figure out is whether or not Eric Reid was supposed to provide some help.
We'll check with the coaches film later this week, but if you look at the GIF, you can see Reid sort of standing there deep down the field. It seems like he could have slid over and help Ward. We can't know who had what role with certainty, but that's at least how it appeared. My guess is Vic Fangio will be asked about it later this week, and/or one or both of the players will comment on it after the game.