The bonus score in the 'Bonus Score Defense' attribute attached to the Point Breaker card includes all extra points acquired excluding points gained through the following (considered separate)
- Distance, Scoreboard, Floating Skill Icons (Skill OBJ), Stuatues, Figurines, Foul Posts, Signage, Announced Home Runs, Cycling Home Runs
The 'Bonus Score Defense' attribute will reduce the amount of bonus score damage your opponent incurrs on you by a specified percentage (e.g. 120% -> 60%).
Unlike other defense attributes attached to 'Shield'-type skills (Score Shield, Iron Shield), penetration effects do not apply to the Points Breaker card since it only defends against 'Bonus Score'.
In other words, the Point Breaker card has an advatange over shield cards since Lucky Drill and Rocket Bat cards can't penetrate its defense bonus!