Red #1 is forcing Blue #1 forehand.
Blue #1 swings the disc to Blue #3 and starts to cup upline to the empty cone. Red #1 tries to get their body in the way to stop the cut.
In this case, Red #1 was able to stop a dangerous upline cut and only give up a short throw. The thrower's momentum is going toward the force sideline and the mark is on - the offense has only gained a very small advantage.
(reset)
If Red #1 can't get their body in the way, but has the speed they can undercut the throw.
And catch their D
(reset)
What Red #1 doesn't want to allow is the upline with momentum going forward
Roasted upline
(reset)
If Red #1 starts to cheat and anticipate the upline, Blue #1 throws a force side fake.....
....then breaks them to Blue #2. In this drill, the thrower shouldn't look to the break as the first option. It's just there to keep the mark honest.