Instructions
Enter the Safari Zone and walk through the different zones in search for Scyther. Make sure to walk through the tall grass, as wild Safari Pokemon tend to hide in those areas.
Throw either rocks at the Scyther to make it angry or bait to make it stay longer. Hurting the Scyther with rocks will make him easier to catch, but it also increases the chances of it running away. The bait will cause no damage to the creature and will make him stay longer.
Throw your Safari Ball. You may not capture him, but if you are lucky he won't run away after the first attempt. The rocks will damage him to give you a better chance at capture, but you may only have a few chances.
Once you have captured the Scyther, it will be sent automatically to Bill's PC, which you can access from the Pokemon Center. You can retrieve it there.