If you haven't gotten Jecht Shot from the minigame before Luca, you might as well move on; you'll only get a Strength Sphere for your trouble. The Strength Sphere, after placing it in an empty node, gives the activator +4 strength. Wakka might score a goal with a Venom Shot but it's a long shot getting pass the defenders.
If you did manage to score a point, retake the blitzball from the Goers and just sit your player at your goal; the AI is dumb and generally doesn't understand your player is sitting at the goal.
Also, play in manual; auto is a bad idea in blitzball.