When a rotated die collides with its normally-oriented companion, it leaves rotated clash marks on the opposite die.  Naturally, the clash marks it picks up look rotated as well.  Ordinarily it is impossible to determine which die was rotated.  Only in the case of complex and compound rotated die errors is it possible to identify the culprit, and most of the time it is the hammer die.

    This 1984 cent shows a modestly rotated set of clash marks, amounting to 15 degrees.  The coin was struck while the die was still in its rotated position.

    The bottom picture (the reverse of the coin) has been inverted and horizontally flipped to show the correct attitude of the die when the clash was created.