Most fields are not open on Weekdays unless you have a private group. The only time that I know if a paintball field is open is unless their is a national holiday on a weekday i.e. Memorial day, Labor day, etc.
Exit the 15 Freeway on Camino Del Norte and turn left. Camino Del Norte becomes Twin Peaks Rd. Turn right on Espola Rd. then left on Poway Rd. Turn left onto CA-67 which turns into Main St. Turn right on Dye Rd. Take a left onto Ramona St. then finally a right on Warnock Dr. You will see Velocity Paintball Fields sign on your right hand side.
If that doesn't help call the Bonita store at:
I've played all the fields in San Diego and in the north county and I feel Velocity has the best fields ( Hyperball, Air Ball, Speedball, Woods). Also the park has a rookie and advanced walk-on group. The park itself is really organized and clean. I cannot express clean, as I've been to many "other" parks and it feels like I' was playing on a city dump ( I'm not going to name any names).
If there are any question just ask or call the store.