Sentinel
Source: Player's Handbook
Prerequisite: Level 4+, Strength or Dexterity 13+
You gain the following benefits.
Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20.
Guardian. Immediately after a creature within 5 feet of you takes the Disengage action or hits a target other than you with an attack, you can make an Opportunity Attack against that creature.
Halt. When you hit a creature with an Opportunity Attack, the creature’s Speed becomes 0 for the rest of the current turn.