As noted above some actions are both offensive and defensive. In the middle, by moving the balls to your offensive zone, you are fueling an offense, but also denying them to the opponent, thus said action is both. Also, the act of pinning can be used for both (stopping someone from pushing a ball in or keeping them out of the way of a shot).
As for offense/defense in general? It depends on your thinking. Obviously if your alliance can’t score, you can’t win, which would suggest offense. However, on the flipside, if the opposing alliance can’t score, it can’t win, suggesting defense.
The one thing that I’ll say is that a lot of the time, defense gets overlooked. It has no really measurable characteristics. Sure you can count how many blocks it makes, but how much value does an action like pinning add? Because you’re looking for the absence of opposing scoring it’s hard to quantify defense.
Offense is much easier to measure since it is just “how many points can they score.” This will probably get more attention from teams, but likewise, many teams will be doing it, and to stand out, you will have to be quite good (although this is true in any case).
As an example, in the 2008 game, Overdrive, I was wondering the entire Championship (and even before that) why some teams didn’t play just to “harrass” (play defense) because they couldn’t hurdle. I think it was certain penalties to be avoided, but in the end, it could make a huge difference (if you’re familiar with the game, if I were to punch your trackball back over the line after you crossed, you had to go around once and take it back around before you could get points for it again). Almost every alliance picked based on points scored, which ignored that there were only two game pieces for each alliance to score with. At the end when I was getting on the bus, a group was walking by talking about how they should have picked a lap bot that could run and annoy the other team.
Defense is great, but often doesn’t get the attention it deserves (although by the nature of this game, it very well might).