Wouldnt count on it. Hagler took shots from the likes of Cyclone Hart Hearns Mugabi Briscoe so ill say no.
Taking a shot has more to do with anticipation than anything else. Hagler was a near perfect technical boxer with exceptional balance. He knew what was happening and what to do next. You can't go into the rain and not get wet. Hagler got wet but he saw everything coming. Very hard to hit clean or tag him when he wasn't rolling with the blow. So in answer to th question. No. Julian Jackson is not knocking out the guy better fighters couldn't tag clean. However, Put a blind fold on Hagler and he gets knocked spark out. Just like everyone else would.
No Jackson had great power but Hagler has an ATG chin. Like Mike McCallum, Hagler would soak up Jackson's best and then counter. Jackson, not nearly as resilient as Hagler, an defensively dificient, would get tkod by the middle rounds.
Without anticipation, a flush shot on the chin from Jackson should KO every person on the planet, including Hagler.
Hearns had comparable power to Jackson imo. I don't think one JJ shot would KO Hagler. But there are always freak KOs. Usually, iron chinned fighters can always take some punches from the hardest punchers around.
Hagler had an iron chin and a solid defense with good head movement and parrying skills, it's unlikely he would get hit with a perfect shot he didn't see coming. If Jackson somehow managed to hit Hagler with a perfect blind shot, like the one on Graham, then yeah, I think even the steel chin of Hagler gets dented here and he gets knocked out. Jackson had that type of freakish power.
I never understood what the significance of knocking out a poor defenseless horse meant. he sure didn't knock out Hearns.
I don't see Hagler knocked out by Jackson. The punch he took from Hearns was the hardest I saw landed on him and he was rocked, and he came right back. I think Hagler takes the punch and comes back and stop Jackson similar to how McCallum did.
Michael Nunn one punch ko normally iron chinned Kalambay who had defeated McCallum and Barkley. Would a freakish one punch ko Hagler ? The only scenario i see it happening is if Hagler moves up to LHW and faces a Bob Foster type fighter.