#4 The Rock intentionally gave Mankind a concussion
Professional wrestling is a dangerous sport, and that is why wrestlers do everything in their control to prevent a tragedy from happening. However, during the Attitude Era, some wrestlers went overboard, attacking their opponents with steel chairs and doing other dangerous stunts.
In 1999 Royal Rumble, The Rock handcuffed the arm of Mankind behind his back and hit him 11 times with a steel chair on his head. The injury was so serious that Mankind went into a concussion and passed out. This was definitely one of the most violent and dangerous stunts in the history of WWE.
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#3 Roman Reigns got booed out of the building
If the 2014 Royal Rumble was known for getting negative reactions by the audience, the following year's Royal Rumble PPV went a notch higher in getting a double dose of negativity. Fans wanted Daniel Bryan to be the winner hence started chanting his name from the start, but Bryan was eliminated quite early. This did not go well with the audience.
When Roman Reigns entered the ring, the crowd started booing him. As he fought, the crowd grew impatient and made sure the winner left the ring only after getting trolled mercilessly. An appearance from The Rock also could not salvage the situation.