He was pretty active during the early rounds, but it's hard to out-work someone who literally throws 90 punches a round during the first 5.
The guys who were "impossible to beat" were obviously the ones who retired at the top, unbeaten, like Rocky Marciano, Gene Tunney, Carlos Monzon, etc., and maybe a few more, just a handfull, (not to be confused with guys like Sven Ottke, for well known reasons).
Hardly anyone out thought Marvin Hagler. The one time if you could call it that was against Leonard. But me i thought that fight was to close to call.
Erm, getting back to the topic... I don't think anyone at middleweight could beat Dick Tiger in a pure slugfest.
Yeah Willie The Worm may have the only one to really beat him but a prime Hagler 80-85 was tough to beat.