And then quite suddenly in another flash, as if lifted by a new strength and resolve, he leaped.
No great leap for a man, but a leap in the dark. Straight over Gollum’s head he jumped, seven feet forward and three in the air; indeed, had he known it, he only just missed cracking his skull on the low arch of the passage.
Gollum threw himself backwards, and grabbed as the hobbit flew over him, but too late: his hands snapped on thin air, and Bilbo, falling fair on his sturdy feet, sped off down the new tunnel.

Chapter 5 Riddles in the Dark