1 No- it's not substitute. I would interpret it as meaning that Ashavin had set the chance up by passing the ball to him, but I don't follow football and it may have a more precise meaning.
2 If you take a knock, you are hit and hurt in some way.
This means that he made a hole in the goal net when he blocked the shot.
When he cleared the shot, his side did not fall behind- the score stayed at 0-0- if he had missed his team would have been 1-0 down.
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