It's just part of the 'Cambridge thing' isn't it. Does anyone know which colleges in particular?
It's not tradition, it's to keep the lawn in good condition. It's basically all of the old colleges. John's, Trinity, Corpus, King's, Queens', Emma, Christ's, Magdalene, Selwyn, Clare, Trinity Hall, etc etc.
Most colleges have some lawn space for you to walk about on/sit and eat your lunch. In the case of Queens', it's the lawn that backs directly onto the Cam, which is very pleasant in the Summer time.
The rule of thumb is usually that if it's in a court, you cant walk on it! (although fellows of the college are I think - at least at my college they can). But yes there are exceptions, and some colleges seem to have more grass you can walk on than others....Emma being a key example! But colleges like trinity and kings have fellows gardens which you can use I believe, it's just not right in the middle of college grounds that's all
As for which colleges it applies to, it's the rule rather than exception that you shouldn't walk on the grass. Most colleges have somewhere where you can sit, but NOT in the middle of the courts!
Some colleges aren't fussy - Newnham is one of them (except in the depths of winter, when trampling the grass would just turn our lovely lawns to mud. If you have any gardening knowledge, this is common sense. Or, a more 'hip & happening' way of putting it: your shoes will get soaked and muddy...*grins*).
I've heard that if you do, the ghost of Isaac Newton will come get you and drop apples on your head. And if you throw them back, you get a scholarship.
We're not allowed on the front courts (which are admittedly tiny), or the Master's Garden, which is effectively their front lawn. We can sit/sunbathe/play croquet/whatever on the rest, so I don't see the problem. Fellows are allowed where they want I think.
Tradition, keeping them looking neat, sheer bloody-mindedness of College... it varies.
In Clare, there's four little lawns in Old Court which are out of bounds to everyone (including Fellows) apart from gardeners. Tourists normally last about 20 seconds on the grass before asked "Come off the grass, PLEASE!" in increasingly firm tones by the porters. Other than that, the rest of the grass is free to walk on.
At Kings a few years ago, a couple of undergrads played a nice trick. In summer, in front of a load of tourists, one student (whilst dressed as a tourist) walked on the grass in front of the gate. Another student, dressed asa porter, came runnign out with a fake gun and "shot" the "tourist". Apparently it traumatised a large number of watching people!*
* - NB. I think this is true- at least the bare bones of it. All kind of embellishments circulate around.
If you stand on the grass at Newnham or New Hall when you're not supposed to, you develop wellingtons that are impossible to remove, a Fernando Torres-style haircut, big muscles, overalls that seem grafted onto your body and within 2-3 minutes, you will have become a gigantic lesbian. This happens regardless of the felon's gender.
Just a friendly warning to any potential rule-breakers.
It's nothing to do with what century we are in. If a rule is being broken for the sake of breaking it then people generally aren't amused. I honestly can't believe you're being serious in suggesting that a college might be amused by people camping on their lawns.
Once again not walking on formal lawns is not an exclusively Cambridge thing, and nor is it the reserve of old-fashioned institutions. It is to preserve the lawn.
Strangely though, when it snowed everyone (including the porters for several hours until they eventually threw us off) ignored this completely for the sake of snowball fights/snowman building, even though presumably skidding around in the snow was more likely to damage the lawn that in any other weather conditions...