Source: https://www.descentbb.net/viewtopic.php?t=14791

USB pin 1 (red, Vbus) –> GP pin 1 (5V)
USB pin 2 (white, D-) –> GP pin 14 (BY2)
USB pin 3 (green, D+) –> GP pin 10 (BY1)
USB pin 4 (black, GND) –> GP pin 4 (GND)

USB shield –> GP shield
GP pin 2 (BX1) –> GP pin 7 (BX2)

Gameport pinout #