Any cards you didn’t play remain in your hand. You can’t have more than four cards in your hand at the end of your turn, unless a special ability grants you a larger hand size, but you can acquire more cards in your hand after your turn (e.g. buying cards from a discard pile).
Developer’s Notes
At the end of your turn, you can have no more than 4 cards in your hand. During the Jobber Security phase of your turn, you can discard as many cards as you’d like. Most of the time, these discards will go to the appropriate discard pile, Gear or Ring, but when there are higher-tiered players discarding while opener-tiered players still exist, the discards will go directly to those players in order to help catch them up.
The Bodybuilder Gimmick allows you to increase your hand size by 2 cards for every Crowd Point you spend to activate the ability. So, if you had 7 cards in your hand at the end of your turn, you could spend 2 Crowd Points to increase your maximum hand size from 4 to 8 and keep all your cards.
Every wrestler has the ability to discard a Gear card in exchange for a new Gear card, drawn face down. This ability has a 3 Crowd Point cost. (See the reference section on your play mat)
You can acquire more cards after your turn ends without having to discard back down to 4.
Heels have the ability to buy the top card of the Gear discard pile for 2 Heat, and Faces have the ability to buy the top card of the Ring discard pile for 2 Pop.
Sometimes, a player will discard several cards at the end of their turn, and someone will buy one right up from a discard pile. A player can even buy back a card they just discarded after their turn is over.