he might be able to stun him, but hagler defence was too good to be caught by a really flush shot from Hawk and then it might not do anything. It would probably damage Jackson more than it would Hagler Look at the great right that Hearns landed on Hagler. it did more damage to him
Julian Jackson could affect anyone in the history of his divisions, but I don't think he knocks Hagler out, Marvin's defense and chin are far too good for that. Jackson probably stuns Hagler early like Hearns did, but I don't see it going 3 rounds, probably not even two. Prime Hagler would take him out quick.
Hagler had slowed down incredibly by the time of Mugabi, though. What if Jackson was connecting cleanly?
If he landed a great shot, then sure. He could stun, hurt, or drop Hagler. Hagler had an iron chin, but this Jackson we're talking about. It all depends on how hard the shot was, if it came at an angle where Hagler couldn't see, the timing, the placement, etc...
Prime Jackson was a JrMW. When he hit Hagler "it would hurt him". When Hagler hit Jackson, it would really hurt Jackson. Hagler would probably get cut and wobbled, but when he started landing that left hand, and a few marginal ones at the waistband, he would probably wear Jackson down to a 12th round stoppage. Afterwards, he would say "Hearns & Jackson were my two toughest fights, and I am packing it in and heading to Italy."