The battle for midfield supremacy
A big part of the reason Sheffield United had the better of the first half was their sheer numbers in the middle of the park. Manchester United won no clean second balls, everything was contested and Sheffield often came out on top in a physical contest.
Fred and Andreas Pereira found themselves in an uphill battle going up against Lundstram, Norwood, and Fleck in the middle with McGoldrick dropping in to support them. Juxtapose that against a static Antony Martial, some fairly aimless movement from Marcus Rashford, and Daniel James holding his wide position, meaning that the midfield duo were isolated.
The second half saw two key changes in the system, Jesse Lingard replaced Phil Jones to make it a midfield three and the forward line dropped a few metres closer to the midfield. That nullified Sheffield United's numbers and allowed the likes of James and substitute Mason Greenwood to take on players, while Martial could drop into spaces to receive the ball as Sheffield were pushed back.