Here's a wonderful photo, pulled from the archives by historian Michael Beschloss—Babe Ruth knocked completely unconscious by a collision with a concrete wall.
The date was July 5, 1924, and the Yankees were in Washington's Griffith Stadium for a double-header with the Senators. (It was already New York's third double-header in four days—they would play 10 before July was out.) In the fourth inning, Joe Judge lined a ball just into the seats down the right-field line. Here's how the next day's New York Times described it (Headline: "Yanks Break Even And Fail To Advance; Ruth Knocked Senseless") :
The Babe ran into the pavilion parapet with the full force of his body, and dropped unconscious to the grass. Uniformed policeman ran to his assistance and kept back the crowd that seemed disposed to leave the chairs and get a close-up of the injured warrior. Several photographers happened to be on the spot and they snapped the Babe as Trainer Doc Woods ran up with the water bucket and the little black bag of first aid preparations.
At first it was thought that Ruth had been knocked out by a blow from the concrete on his chin, but it was sooon discovered that he had been knocked out by a jolt in the solar plexus. His left leg was also hurt at the hip.
This being 1924, they splashed cold water on Ruth's face to wake him up. Manager Miller Huggins wanted to take him out, but Ruth refused, finishing the game 3-for-3—and playing the second game of the double-header, despite a noticeable limp. Ruth would start every game that season.