1/2 cup chopped seedless watermelon, or as needed
3 fluid ounces light rum
1 fluid ounce lime juice
1 fluid ounce simple syrup
3 fresh lime wedges
Blend watermelon in a blender or food processor until smooth.
Fill a shaker with ice. Pour 4 fluid ounces watermelon puree, light rum, lime juice, and simple syrup into shaker; cover and shake. Pour cocktail and ice into a pint glass and garnish with lime wedges.