#3 Zelina Vega's concussion
This one is a somewhat recent entry to the list. At WWE Evolution, Nia Jax, Zelina Vega, and 18 other female superstars were part of a 20 women over the top rope battle royal. The winner of the battle royale would earn herself a future title opportunity of her choice.
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Nia Jax was dominant throughout the match. The last 3 participants of the match were Nia, Vega, and Ember Moon. Thinking she had won the battle royale, Vega began celebrating. However, Nia picked Vega up and threw her outside the ring onto Tamina. The landing was horrible - giving Vega a concussion in the process.
#2 Not catching Charlotte
On the 10 April 2017 edition of RAW, Nia Jax was scheduled to face Charlotte Flair. Halfway into the match, Charlotte attempted a moonsault from the top rope onto Nia who was outside the ring.
Moonsault is one of the riskiest moves in wrestling, and requires immense coordination from the receiver to break the fall. However, Nia failed to do so - resulting in Charlotte landing face first onto the floor.