It says in the rules that even if an innertube is deflated it is still in play, so they are expecting some to go flat. Is it illegal to un-/intentionally pop one?
Yes, it is illegal to intentionally pop one.
**<G55>**Deflated GAME PIECES - A GAME PIECE that has been deflated is evaluated the same as one that is inflated when determining the match score. Intentionally deflating a GAME PIECE is considered field damage (see <G34>).
If you unintentially pop one it should be ok. However, they have strict rules about intentially damaging the field
Unintentional damage is expected through regular play. Though repetitious incidents from the same team may be called by the refs and sharp or hazardous edges/parts of a machine will be called by the refs to fix prior to a teams next match.
I would love to cite a rule, but I can’t seem to find one.
The way I understand it: popping a game piece is field damage, and so it is the judges’ call–if they think your 'bot poses a threat of popping game pieces, they will make you fix it. If they see you pop a ridiculous amount of game pieces on the field, they’ll probably shut you down. But they expect there to be a lot of deflated tubes, and they probably won’t penalize you at all if you accidentally drive over one and it pops. Just don’t do anything foolish, and you will be fine.
You might consider submitting to the QnA if nobody else posts a definite answer.
JBot
EDIT: Well, a lot of people beat me. Oh well.
Darn it! I had an idea in the makings that was just shot to pieces. Well, it’s a whole lot better to know now rather than later. Thanks!
Just curious but WHY would you want to design your robot to intentionally pop the tubes?
I was thinking that it might be useful if you could build an extension that deflates the innertube. If the other teams are busy focusing on how to manipulate the tubes when they are inflated, this would create an advantage. Well, that’s out. Just tyring a bit of creative thinking on my part…
That’s genius! Too bad it’s illegal.
To Fit more on a spider rack.
Imagine this. You are blue. You put a blue one on a rack, red comes over and puts a red one in front of yours.
In a normal “inside the box” way of looking at things, you just lost that position.
What if you popped a spoiler and placed it over the red ring? 
*
Or popped a blue and put it in front of the red ring now giving you back your scoring position. *
With popped tubes being all over the place I can see this happening legitimately. - A team picking up an already popped tube and placing it for a win.
How the refs will decide on this will be interesting.
They can either say
A) They count and is just a loophole no one thought about yet (until this post)
B) Popped Tubes won’t count. (going against the current rules, and causing havoc in week 2 or more.)
I don’t envy the position of the GDC right about now.
*No I don’t condone popping of tubes intentionally.
I’m just saying it could happen in a scenario where there are popped tubes laying around on the floor.
(And yes, that will happen. Tubes will pop and they will be laying on the floor - ready to be grabbed).
For purposes of determining the ownership of a spider leg, only the innermost tube counts – speaking generally. The situation as described above would still result in the spider leg being scored for the blue alliance, despite the presence of a red ringer.
See pages 12 and 13 in The Game for a breakdown of how most circumstances will be scored.
The only way to “take over” a spider leg, meaning to have it score on your own alliance, would be to place your own ringer over a spoiler, which would mean placing a spoiler over the opposing alliance’s ringer, then pop one of yours and put that over the spoiler.
I’m sure if a tube is popped, and this event happened as said above, the refs would not count the popped ringer over a spoiler and the call will stand as that whole spider leg negated for points on either alliance.
… Only the first two tubes on the spider leg count …
7.2.1 Definitions
SCORED: a SPIDER LEG is considered SCORED if one or two GAME PIECES are HANGING on it in a legal configuration. Based on the particular configuration of the GAME PIECES (as defined in Rule <G57>). The SPIDER LEG may be considered SCORED for the “Red” ALLIANCE, for the “Blue” ALLIANCE, or “Null”.
**<G10> **SPIDER LEG loading - A maximum of two GAME PIECES may HANG from any one SPIDER LEG. While it may be physically possible to force a configuration in which additional GAME PIECES may be supported by the SPIDER LEG, only the first two will be considered HANGING when calculating scores at the end of the match. All additional GAME PIECES on a single SPIDER LEG will be ignored.
Thanks. I know it stated somewhere officially that if more than two tubes were on there they would be ignored.
Well, I was just trying to figure out different strategies for the game and that just popped into my head.