I'd have to watch the replay, but I thought Dee Davis ran the baseline and popped up for the 3. If so, there was no option running below/above the screen.
Well, I just happened to watch every step of that whole sequence in super slow motion multiple times when I got home from the game. Here is what really happened. Cobb was chasing Davis along the baseline at the same time that Shaq was chasing his man from the other direction. As all 4 were coming together, Shaq clearly points to his man, I'm assuming to tell Cobb to switch. Immediately Cobb stops and starts to take a step back to switch to Shaq's man, Inexplicabaly, Shaq doesn't switch off to Davis. He hesitated, and then went on forward to continue to chase his man. Cobb sees Shaq not switching off, and by that time he had lost a couple more steps to Davis, who had already got around his teammate who was screening for him. Cobb did in fact go under the screener, but he was trying to cut off some distance hoping that Davis might spit out on the other side of the screener. Davis did not continue around the screener. He stoped and shot from behind the screen. Shaq definitely hung Cobb out to dry there.