You are able to take one reaction each round of combat. You can take one of the reactions presented here, a reaction you gained from your class or a special feature.
Whenever a hostile creature within 5 feet of you is targeted by an attack roll you can use your reaction and attempt to distract the target. When you do so, you must make a Performance check against the target creatures insight. On a success, the creatures awareness is reduced by 5 until the end of the turn.
Whenever an allied creature within 5 feet of you is forcefully moved or knocked prone, you can use your reaction and hold the creature steady. When you do so, you prevent the target creature from being forcefully moved or knocked prone.
In a fight, everyone is constantly watching for a chance to strike an enemy who is fleeing or passing by. Such a strike is called an opportunity attack.
You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.
You can avoid provoking an opportunity attack by taking the Disengage action. You also don’t provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction. For example, you don’t provoke an opportunity attack if an explosion hurls you out of a foe’s reach or if gravity causes you to fall past an enemy.
Whenever an allied creature within 5 feet of you is targeted by an attack roll you can use your reaction and intercept the attack. When you do so, the attack roll is made against you with advantage.
Whenever an allied creature within 5 feet of you begins its turn within 5 feet of a hostile creature, you can use your reaction to switch spots in an attempt to save your ally. Your ally must have a movement speed greater than 0 to be saved. When you do so, you and the chosen ally switch places.