well, it's really all left up to the discretion of the official score-keeper.
in most cases, if a player receives a pass, then works on his own to get into scoring position, it is not an assist.
entry passes to the post (the the post player posting up to score) are not normally considered assists.
now, in your example, if nash passed to dirk on the post, and he just did a fade away jumper... hmmm... it may be an assist, it may not. again, the official score keeper decides.
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