In Questions of Style and of Theory, I wondered (1) what was the earliest example of the ...Rxc3 sacrifice in the Yugoslav Variation of the Dragon Defense, and (2) how Kasparov categorized Fischer's style.
Unfortunately, I didn't phrase the question very well at Chess.com, and while I got three nice examples of Dragon ...Rxc3 tactical sacrifices, none of them were positional sacrifices of the type in the Yugoslav Variation. One of the examples, however, reminded me that Korchnoi was a longtime defender of the Dragon, which led me to an earlier example of the sacrifice than I already had. In the diagrammed position, Black played 15...Rxc3.
1967 Sousse Interzonal
[FEN "r1r3k1/p2bpp1p/3p1npQ/qp2n3/3NP2P/1BN2P2/PPP3P1/1K1R3R b - - 0 15"]
As for Kasparov, I searched the Fischer chapter in Predecessors IV, looking for discussions of the American's playing style. I found nine passages, of which all but one were Kasparov quoting other Soviet players. Kasparov's remark was a comment to 12...g5!? in Gligoric - Fischer, 1970 Palma Interzonal, where he wrote,
At the start of the 1970s the play on the dark squares appeared rather promising for Black, which attracted Fischer with his very concrete approach to the solving of opening (and also other) problems. This was a step forward: in the era of Botvinnik, Smyslov, and Petrosian, the ...g6-g5 advance, creating a chronic weakness on the light squares, could not even have been conceived. (p.366)
The italics on concrete approach are Kasparov's. When he said, 'For a player of Fischer's style, that's not a very good comment, because he needs to be a little more concrete', he meant exactly what he said -- that Fischer's style was 'concrete'. Kasparov's opinion on Fischer's style is supported by the other players quoted in Predecessors IV, including several examples copied from Russians Versus Fischer by Plisetsky (Kasparov's assistant on the Predecessors series) and Voronkov.