Area 51½ is a secret field in Backyard Soccer that's available for use in pick-up games and penalty kick practices. It is a dirt field that is in the middle of a government airfield, which itself is in the middle of a desert. As its name suggests, it is a parody of the real Area 51.
The only known way to access this field is by editing the hegames.ini file. Under [Soccer], insert area-103-halves-enabled=1.
Oddly, the background noise is the same as the Pro Sports Arena's (large crowds being heard cheering on the teams) even though there is nobody watching the teams play.