Low blow

You have learned a fair fight doesn't always end with a won fight. You gain the following benefits:

• Increase your Strength by 1, to a maximum of 20.
• Whenever you can make an oportunity attack, you can cause a creature your size or smaller to trip as a free action. The target must succeed a Dexterity saving throw (DC 8 + your proficiency bonus + your strenth) or fall prone.