I'd say about 30 to 50% of the teams will be able to score 5 or more balls in the center goal in 40 sec without defense and about 25% will be able to do it with defense.
I know one team which can gather
and score 5 or more in the center goal in 40 sec.
As for how to defend, all a defender has to do is push against the shooting robot enough to move them a degree or two per second to significantly reduce their percentage in manual mode. On the other hand, if the shooter has a good camera:shooter servo, it might take blocking or some pretty aggressive defense to prevent scoring.