Actually exchanges like coinbase are just middle man, all buy/sell orders for bitcoin were placed by the users/traders.
If you are talking about some dramatic graph movement than its might be just a visual bug not a real trade. Exchanges are known for technical glitches that's why its not always safe to keep your coin in exchanges.
Coinbase is a registered entity so you can file a case against them if you like to and if you have enough evidence to prove your claims.
Its not the users that caused the price to go down, its definitely the Exchange. Its impossible that more than half users dumped their bitcoin in the 5 min time frame.
From where you got that data, more than half users dumped in 5 min time frame If you are talking about some dramatic graph movement than its might be just a visual bug not a real trade. Exchanges are known for technical glitches that's why its not always safe to keep your coin in exchanges.
Coinbase is a registered entity so you can file a case against them if you like to and if you have enough evidence to prove your claims.