United's Under 23s took home a point away at Bolton Wanderers after being pegged back second half from a 1-0 half-time lead.
United had been relatively in control of the game when Hallam bundled a Harry Sheppeard cross home from inside the six-yard box under pressure from the Bolton defence.
But a header 15 minutes from time by Joe Pritchard ensured a share of the points on a night where either side could have nicked it.
United started the better side and threatened to get in behind the Bolton defence on several occasions, but the first chance came when a pull back found George Broadbent who sliced his effort wide.
In control for large parts of the opening 20 minutes, United looked for the ball in behind the defenders but Simeon Oure was flagged offside when he broke through one on one with Jake Turner.
At the other end, Jordan Amissah had to be alert to push away Jordan Boon's header from a corner and Blades would take the lead just under 10 minutes later.
Great work from Sheppeard combined with Hallam's eye for goal saw the winger's cross find the striker inside the six-yard box, and despite not making clean contact the ball bobbled into the corner of the net.
It should have been 2-0 just minutes later when Oure found Hallam, the striker's neat flick finding Reece York but his low effort was well pushed away by Turner.
United struggled to build momentum after the break, Jack Earing firing an early warning sign just over the bar before Amissah was called upon to make a brilliant save when Matthew Barnes got free on the left and hammered an effort at his near post.
Pressure told with 15 minutes to go as a cross from the right found Pritchard who headed back across goal into the corner, leaving Amissah with no chance.
Bolton continued to press forward but it was United who had a chance to steal it with five minutes to go. Sheppeard again with a dangerous ball in from the right and Oure couldn't quite turn enough to get his powerful effort inside the post.
The hosts could have nicked in the final seconds when Pritchard's effort hit both bar and post but didn't cross the line, much to United's relief.
Blades: Amissah, Williams, Cantrill, Neal (Brunt 67), Graham, York, Sheppeard, Broadbent, Oure, Hallam, Mallon.
Unused: S. Kelly, Gordon, Belehouan, Boyes.