Yes, round 3. That is the round that I've been questioned on before, and I figured someone would question this time too.
Here are the things I took note of in round 3 that ultimately factored into me giving the round to Marvin:
Round 3 starts at 1:49 of the below video.
Hagler starts the round off by stalking the ever moving Ray and looking for a spot to throw.
2:27 -Marvin sees his spot and lands a left hook that landed clean.
2:54 -Leonard throws a looping lead right, which Hagler blocked, but the commentators incorrectly said it landed.
3:03 -Leonard landed a right hook to Marvin's body, Marvin landed a counter left hook. Neither did any damage at all.
3:15 -Leonard threw another right lead and it was once again blocked by Hagler. Hagler missed the counter punches he threw.
3:24 -Leonard landed his first right lead, but missed the left hook he put after the right lead. Hagler dug into Leonard's body with a right hook under Leonard's left hook. In my opinion, Hagler hook to the body had more impact than Leonard's right lead, thus in my opinion Marvin came out the better of the two in the very brief exchange. Gil Clancy called the same view I just posted.
3:32 -Leonard once again throws a right lead, which was slipped by Marvin.
3:46 -Yet another Leonard right lead is blocked by Marvin.
3:50 -Marvin lands two good body shots as Leonard is trying to tie him up. Leonard came right back at Marvin with two right hands, the second of which was the first fully flush shot Leonard landed the entire round. In my opinion, for the first time that round, Leonard came out on top in the brief exchange.
3:56 -Marvin blocks a Leonard right lead. Marvin proceeds to land some light right uppercuts as Leonard tried to tie him up.
4:02 -Leonard misses his right lead again and ties Marvin up as Marvin looked to go to the body again.
4:13 -Leonard threw a right lead with conviction. Marvin slipped it and Leonard tied him up. Marvin landed a right hook to the body as they pushed off from eachother.
4:22 -Leonard finally lands his right lead, but it was grazing.
4:25 -Leonard thew a hard left hook. It was partially blocked by Marvin and also partially caught Marvin behind the head.
4:30 -Marvin lands two body shots, Leonard lands a left hook but misses his right, and Hagler landed a right hook to the body as Leonard was backing off.
4:44 -Marvin threw a lazy jab which Leonard countered with a sharp straight right left hook combo.
4:49 -Leonard threw a straight right-left hook combo, both were blocked and Marvin landed a clean left hook at the bell.
Basically, neither fighter did much noteworthy work, but Marvin did more work that landed than Leonard did. Most of Leonard's attacks were blocked or slipped by Marvin, and most of Marvin's attacks outside of stalking Leonard behind the jab when in range were to the body as Leonard looked to tie Marvin up.
I gave the round to Marvin on activity and overall landing more punches. Hagler also landed the heavier blows, despite very few heavy blows being landed by either fighter.