I was DMing a session a few days ago. The players had defeated some bandits, but one was trying to escape. He was about 200 ft. ahead of the monk, on horseback moving at full movement rate. The monk player wanted to use his turn to run at full speed, and about 40 - 50 feet away from the fleeing bandit, he wanted to leap and grapple him to knock him off the horse. So essentially, run 150 ft., leap the last 50ft. and tackle the bandit on the horse. I am not sure, but I thought that when you are running at full speed (in this case normal movement is 50ft. x 4 = 200) you could not also attack that round. Any suggestions how I should resolve this?