SHAFT (july 2nd, 1971) didn't start the "Blaxploitation" movement. My understanding is that Melvin Van Peebles' SWEET SWEETBACK'S BAD ASS SONG ( April 23rd, 1971) has that honor... Both did change the way movie soundtracks were developed and marketed.

While SSBAS predates Shaft, there are many who credit the latter. Via Wikipedia: "Blaxploitation films were the first to regularly feature soundtracks of funk and soul music as well as a primarily black cast.[1] Variety credited Sweet Sweetback's Baadasssss Song, released in 1971, with the invention of the blaxploitation genre while others argue that the Hollywood-financed film Shaft, also released in 1971, is closer to being a blaxploitation piece and thus is more likely to have begun the trend.[2]"

I can agree that there is a lot of publicity value in a 'Hollywood movie' like SHAFT. There is a point in that Hollywood casting Richard Roundtree gave the project another, hipper, and yes better direction. However, I would point out however that Shaft was initially conceived as a movie for a white actor in the lead whereas SSBAS was ALWAYS conceived as a black movie for the black audience which Van Peebles surmised was being under served by the media establishment. In any case, it is a muddy area of film history with both movies being released so close to one another. I would estimate that SSBAS lit the fuse and SHAFT threw gas on the fire making it bright enough for mainstream audiences to see...

Good point, Bill. Both should be considered as progenitors of the sub-genre. Thanks for that additional background!