Han shot first

From Wikipedia, Han shot first:

In the original version, Solo shoots Greedo under the table after uttering the line 'Yes, I'll bet you have.' In the 1997 Special Edition version, Greedo shoots at Solo from point blank range and misses. Han shoots him in retaliation afterwards. Thus, the phrase 'Han shot first' is a retort to director George Lucas's explicit assertion that 'Greedo shot first.' In the original release of Star Wars, only one shot was fired, and it was fired by Han Solo. The ire of some fans led to an online petition demanding that the changes be retracted.

To put it another way, these fans held the 1977 original release to be canonical but not the 1997 Special Edition.