Cheat List
In order to get these cheats to work, go to the match-up screen (as the game is loading) and press X (first position), Y (second position) and B (third position) the required amount of times to unlock the corresponding cheat:

Log Bat: X (0) - Y (0) - B (4) Up
Rubber Ball: X (2) - Y (4) - B (2) Up
Extra Time: X (1) - Y (2) - B (3) Up
No Fatigue: X (3) - Y (4) - B (3) Up
Rocket Park Stadium: X (3) - Y (2) - B (1) Up
Roman Coliseum Stadium: X (3) - Y (3) - B (3) Up
16 Softball: X (2) - Y (4) - B (2) Down
Unlimited Turbo: X (4) - Y (4) - B (4) Down
Tournament Mode: X (1) - Y (1) - B (1) Down
Mace Bat: X (0) - Y (0) - B (4) Left
Maximum Speed: X (0) - Y (0) - B (3) Left
Maximum Power: X (0) - Y (3) - B (0) Left
Maximum Batting: X (3) - Y (0) - B (0) Left
Small Heads: X (2) - Y (0) - B (0) Left
Wiffle Bat: X (0) - Y (0) - B (4) Right
Big Heads: X (2) - Y (0) - B (0) Right
Pinto Team: X (2) - Y (1) - B (0) Right
Eagle Team: X (2) - Y (1) - B (2) Right
Lion Team: X (2) - Y (2) - B (0) Right
Horse Team: X (2) - Y (1) - B (1) Right
Todd McFarlane Team: X (2) - Y (2) - B (2) Right
Terry Fitzgerald Team: X (3) - Y (3) - B (3) Right