I have mentioned streakers in my forthcoming book on cricket and the law. The "practice" as it were of streaking seems to have started in the mid-1970s, to the point where the American comedian Ray Stevens wrote a popular song on the theme. One still finds the odd incident today despite the novelty having worn off faster than the average streakers' clothes.
From a legal perspective, a streaker would be committing two offences: (i) a public decency offence, usually found under the public order statutes; and (ii) trespass, since they would have no right to be on the field of play.
As to the first of those, I wonder if any might try some of the same arguments as Stephen Gough, the soi-dissant naked rambler, who has been arrested a number of times in Britain over the past few years, and usually deploys human rights arguments. In particular, he argues that it is his right to free expression to display himself in the relevant fashion. Although he has succeeded in establishing that by being naked in public he is manifesting his right of free expression, it has always been held that the public interest outweighs that manifestation of his right, and he has therefore been convicted and had any appeal dismissed.
As to the latter, trespassers can usually be removed with reasonable force, though the question seems to have arisen with the individual on Saturday as to what was "reasonable". A few years ago the following ensued in a cricket match in Australia; it was held, correctly in my view, that the actions of the Australian batsman, Andrew Symonds, was in fact reasonable and he committed no offence:
From about 43 second in one can see why the streaker might have started to regret his actions.