Broadbent touched down twice in each half as Rhinos recovered from an early 6-0 deficit to register a third straight win, thrashing the Centurions 48-18.
The 19-year-old claimed his first Super League hat-trick in the mauling, but he could have been celebrating an even bigger haul having dropped the ball with the try-line at his mercy five minutes before his third touchdown.
Agar said: “Jack should have had five and he knows that too. But he is a super young professional and really adaptable for us this year. He has played full-back, centre and wing for us.
“He is a really good finisher. He has struck up a good combination with Tom Briscoe on that left-hand side. And he is another kid we love having about.”
Tom Holroyd and Sam Walters, both 20, were also on the scoresheet for Leeds, while 17-year-old Morgan Gannon, 19-year-old Liam Tindall and Jarrod O’Connor, 20, played their parts in the win.
Agar added: “What pleased me was the amount of young players coming in and growing with confidence.
“We had three teenagers out there and the average age of side was under 23.
“Over the course of the evening we tried to play some really good football when we were in the right areas.
“That’s not easy when you haven’t had a spine operating together and you have young kids with not much experience under their belts playing in the middle for you.
“Leigh started really well with the shape they can throw at us. But after that we did a really good job.”