I just wanted to inquire about the biggest mistake or blunder by Boris Spassky In game no. 6 against Bobby Fischer.
I am tempted to say "agreeing to continue the match after Fischer's protests!" which some argue was a key psychological defeat. If you're looking for specific moves that were mistakes, there are a few candidates. I haven't looked at all annotations, but have Kasparov's My Great Predecessors, vol 4 handy and looking over his notes, it would be either (notations and comments are his):
- ...d4? "This move, conceding the important c4-square, was rightly condemned by the commentators. 20. ...Nf6 really was better...but the most accurate solution was the continuation 20. ...c4"
- ...Rb8?! "The last critical moment."
The biggest was 36...Qe8. Other than that, 20...d4 and maybe 18...Qf8 could be called "weak" if not outright "blunder".