The Gameshark code that enables the player to capture other trainer's Pokémon in LeafGreen is 4D83B1BF E0F5F507, 8E883EFF 92E9660D, B6C5368A 08BE8FF4, 90B4977C C0151DC2. Players should press the L and R buttons as they release their pokéball to increase the capture rate.
This Gameshark code works on any of the trainer's Pokémon. For example, if the player wants to capture Bug Catcher Kent's Weedle in Mt. Moon, all they have to do is use the code and select the pokéball they want to use. The process works just like a wild Pokémon and capture rates are determined by the same factors.