Separated by a Common Language

I think the second meaning that Chris E is referring to is the "line of scrimmage". Wikipedia does a nice job of explaining it.

http://en.wikipedia.org/wiki/Line_of_scrimmage

Chris E's first meaning is correct, with the addition that usually it's a team playing/practicing against itself. In college football teams often have a spring scrimmage, usually with the first team offense playing against the second team defense and vice-versa.

Then, here in Canada, there's the press scrum / media scrum.

(I wonder why we call it a scrum though, given that rugby is not big here.)

Yes, I [BrE] would certainly say that there had been a fearful scrum in the supermarket in the sense of people rushing round buying things and trying to be next in the queue at the checkout.

I don't know anything about "scrimmage", not having really come across it before, but "scrum" or "scrummage" is definitely something that happens in rugger (which my family always call it, for some reason). Goodness knows what, or when, or why..... I do try to avoid knowing anything about rugby.

(Couldn't resist - word verification is pream, which sounds like pro-am, perfectly proper for games matches!)

For the record Canada I have heard Americans or at least American journalists use scrum the same way.

To expand on Ryan's point, friendlies and scrimmages are not quite the same thing. As with football/soccer everywhere, friendly games are played in the US and that's what they are called. Unless it's completely different other places (which it very well could be, football of any kind isn't exactly my area of expertise)a friendly game is played against other teams for an audience. I think a better generic equivalent for US sports would be an exhibition game.

I feel like I should mention the US-Mexico match last night, but it was neither a friendly nor a scrimmage.

Elizabeth - for politicians? I can't say I've ever seen it on TV. Your most important politicians (President, Secretaries) don't sit in an assembly like ours do, so the press can't surround them on their way out.

True, it's not likely to happen to the President that way, but it very much can to members of Congress (especially after important votes).

So not ritualized the same way perhaps, but yes in functionally the same situation. And occasionally I've heard media scrum used for less impromptu press conferences (in which case it can refer to a situation involving the President).

I can't say I've ever heard non journalists refer to a scrum, so it may be mostly a case of writers searching for a new synonym besides gaggle or huddle. I've certainly have never heard an American use scrum in the way Mrs. Redboots did.

The Scottish surname Scrymgeour is derived from 'scrimmager' - evidently there were some fearsome fighters in previous generations.

(AmE speaker) Scrimmages are often played by players on the same team simply to practice in a more realistic way rather than simply doing drills.

From reading British newspapers, I think that "friendlies" are a little more formal. In football (a.k.a. gridiron), "friendlies - (a term one must admit isn't very tough), are simply called pre-season games.

In Australian Football - that is, the native code - "scrimmage" is, though a little old-fashioned now, commonly used by commentators to describe a general tussle for the ball involving a number of players. It's not used in any sense of a practice match or session, though perhaps within the rugby codes it may be - I wouldn't know.

"Scrum" is restricted here to its uses in the rugby codes and in describing a media pack. "Scrummage" is hardly ever heard.

To expound a bit on Matt's comment, a scrimmage [AmE] refers more to practicing a certain part of the game, as opposed to a practice game, i.e, BrE Friendly, AmE Exhibition game.
A typical scrimmage, either against one's own teammates or another team, consists of a series of artificial situations where the players get to practice certain skills, plays, etc.

Scrimmage is rare in British English, but does survive tenuously in the rather splendid song still sung by supporters of Norwich City FC (that's proper football), "On the ball, City", which dates back to the 1890s or so; the chorus runs:

"Kick it off, throw it in
have a little scrimmage
keep it low, splendid rush
Bravo win or die!
On the ball city!
never mind the danger
steady on, now's your chance
Hurrah we've scored a goal!"

Rugby League is the better code.

It occurred to me that it could have been an American typo at some time early last century, as "i" and "u" are next to each other on the qwerty keyboard.

@Patrick:

Did you read the article? "Scrimmage" is the older form.

scrim and scrum have different meanings both sides of the atlantic and there is no disagreement across the atlantic - lines of scrimmage have exactly the same meaning in soccer, rugby and american football. The fact that a line of scrimmage in American football is used in enforcing a rule designed to prevent scrums is just a very awkward coincidence! The only time I have seen misuse of "scrim" is in the PC game AOE3 where Sulieman talks about armies being pushed into the scrim - scrum would make much more sense in that context except that both terms, scrim and scrum post-date his era by several hundred years. Scrim is of late industrial era origin whereas scrum is just a bit later and has nothing to do with scrim at all.