User blog comment:Dave55811/"Coordinate" bets, anyone?/@comment-24.217.239.232-20140304022542/@comment-179280-20140305093509

@ Yes, it's unexplained why Eren attacked Mikasa, but by examining the full scene, you can get a grasp on why did that happen.

Remember that Titan Shifters need a clear goal to start the transformation? Well, Eren didn't have one at the moment, and he wasn't even sure if he was gonna be able to transform at all. But at that time, he had gone through his first transformation and his body was really weakened as a result, so it made Mikasa really worried. We already know that this pisses Eren off, because being protected by Mikasa, means that she considers him weak in his eyes, so excessive attention by her was really bothering him. It's obvious that if he lost control of his Titan body, it would go on to execute his first thought in mind, and if this was being pissed at Mikasa, attacking her would be a given.