My daughter was traversing the tire portion of the obstacle course, when my youngest son went to try the obstacle course. He thought he was smaller than the first horizontal log. He misjudged when he ducked and he hit the horizontal log. That didn't deter him, and he continued ducking under the other logs. Until he got to the penultimate log. He was so happy, he was near the finish, that again he misjudged the last log. It was a loud thud which we heard about 50 meters away.
He didn't cry. He just ran to his mom.
And then cried in her arms. He got a nasty bruise, practically just a scratch.