From I-95 in Wilmington (north or southbound),get off at Rt 52 / Delaware Ave. At the first light (Delaware Ave) turn onto Rt 52 N (away form downtown). At the next light, bear slightly left ... Rt 52 N becomes Pennsylvania Ave. Proceed approximately one mile. Stay right. When you see the University of Delaware / Wilmington Campus on your left, slow down and look to your right for Tower Rd (a very small green street sign). Make a right onto Tower. Go two blocks and at the second stop sign (W 19th St), you'll see the entrance to Rockford Park immediately ahead.
Enter the park and not 50 feet ahead the road (now Tower Dr) becomes one-way to the right. Make that right and you'll see the field 100 yards ahead on your left. Park near the tennis courts to keep foul balls from hitting your car.
The return trip is a bit trickier: Proceed along Tower Dr (one way road), making sure you make a left at the 3-way intersection 1/4 mile past the ball field. Tower Dr continues in a large counterclockwise circle, leading all the way back to the park entrance. Now you're pretty much "in reverse" of the way in. Stay straight on Tower Rd and make a left on Pennsylvania Avenue (Rt 52 S). Look for signs to Rt 95 North (toward Philly) or South (toward Delaware Memorial Bridge).