There was a battle with Mikasa, Levi and Annie's titan form while they were fighting, Levi stepped badly on Annie's titan hand, causing him an ankle injury.

Now when they are all on their horses, and recolecting all the dead bodies up, his ankle is hurting terribly, he's touching his left leg every once a while, you wondered what was wrong, he still had the cold, stoic and unemotional expression though, not showing pain.