You're reacting a bit to the slomo replay. Samuel did a good job and cut him off as he tried to drive - but after there was some hip-to-hip contact, the Terp guy stopped and popped as the bump knocked Samuel off stride a little. That's a tough play to get your momentum going back forward to contest - especially when you're young and haven't gone through all the agility drills with chairs and cones to get your body trained to change direction on a dime. Best you can do is sort of wave your hand in the air while nailed to the floor, but you won't get in the shooter's field of vision. A Ricky Moore type might be so agile that they can spring back instantly and not give that shot up as easily, but those guys are hard to come by.
The issue with needing Boat out there, especially without Bazz, was better seen when Samuel had the ball poked away with 20 seconds left. It just went o/b, but you need better ball toughness there when the other team is going to be gambling and poking at it.