The best back and forth displays of infighting, no one sided master classes: My pick, Whitaker vs McGirt
The Stevie Johnston vs. Jose Luis Castillo fights are good in this regard. Stevie Johnston and Cesar Bazan I too. Castillo vs. Corrales as well, though with a bit less technical precision and more brutality.
Nelson-Fenech I have some extended sequences of top quality stuff...but for the most part it wasn't evenly matched.
Always wanted to see Chuvalo Vs Bonavena which i gather, unsurprisingly was Toe to Toe - Bonavena - Frazier (1st) of course springs to mind Bennie Briscoe vs Eugene Hart - The War Draw Gomez vs Pintor Frank Animal Flecther Vs Ernie Singletary was a minor Slugfest
Most fights involving the likes of Gaspar Ortega, Jose Stable and Charley Scott will show you some good infighting in evenly poised matches. Those guys loved to stand in close and go to work. Touching gloves didn't signal the readiness to engage for them, standing within arm's length of their opponent with their feet planted did. It's a pity there aren't more fighters of that ilk anymore. James Toney was probably the last really good one.... Of a fight of more recent vintage that had some good even exchanges on the inside, Frankie Randall vs. Julio Cesar Chavez I and perhaps even II probably qualify. Another good infighting scrap is Julio Cesar Vasquez vs. Aaron Davis. Vasquez vs. Castillejo had some bruising exchanges as well, though imo Vasquez mugged him a little on the inside...
Really, it wasn't as toe to toe as you might think. Bonavena used a surprisingly effective "boxing" style, and at times looked like a clumsy heavyweight Willie Pep in there.
RED - I think you have just made History ! - Mentioning Willie Pep and Oscar Bonavena in the same sentence !!