I am afraid I don't know any more about the reason Meredith Hunter was attacked than appears in that account. I would assume it is mostly because (s?)he was black (Hell's Angels are often seen as being racially prejudiced).
I have done a bit of a search using Meredith Hunter's name and although I wouldn't trust everything I read on the Net where the gender of this person is mentioned they all refer to Meredith Hunter as a
man. (The article I referred you to just mentions a 'fan' and I had assumed Meredith was a girl's name)
If this person was male that actually makes more sense since the article points out that he was with a
white girlfriend and also that he was armed with a pistol. These two things together would antagonise the Hells Angels who were acting as security guards at the concert. NB A racially mixed couple would have not gone down well with the Angels and the gun would be seen as a threat. (BUT ... See second link below)
Some more links:
http://music.yahoo.c...-Rolling-Stones
http://pages.eidosnet.co.uk/johnnymoped/mu...k_altamont.html
This site goes into a lot of detail about the incident and answers your question. However, I have absolutely NO IDEA AT ALL how trustworthy this site is and it is clearly a very one sided account. Anything that
you write about this incident should show an awareness of that and you really ought to try to cross check this account against others (as all good historians do!)
Try searching for "Meredith Hunter" +"Rolling Stones" yourself in order to find more links and accounts so that you can cross-check.