Now that we moved from the U.S., there’s a great deal of soccer on TV. I always thought that games were 90 minutes, yet it seems that there is a variable amount of time added to the clock at the end. Why is that?
Also, just after observing for a few months, it seems that whenever there seems to be a collision, which ever player is blamed seems to argue about it with the referee. Are these arguments a constant thing?
Injury time.
Time is added on for stoppages such as injuries or substitutions. A typical rule of thumb is that the time-keeper will add thirty seconds for each substitution. A major injury or a sending off might consume many minutes. A game I watched recently had 9 minutes of extra time.
On top of that there is also a tradition that if one of the teams is Man Utd and they are a goal down at 90 minutes one has to add as many minutes as it takes for them to pull level otherwise Sir Alex will throw a fit.
Why can’t they have an official (off field) timekeeper, who can stop and start the clock as necessary - like in American football?
No particular reason, they just don’t. The general idea I suppose is to keep the game flowing as much as possible, and manually stopping and starting the clock might militate against that. I do agree though that the amount of time added on bears only the loosest correlation to the time actually lost to injury stoppages and substitutions.
Regarding arguing with the ref, this season they’re trying to stamp this out with a “Respect” campaign at all levels of the game. It’s not going so well, though, because of idiot managers and pundits who trot out the bullshit line “respect has to go both ways,” whenever a ref makes a mistake, and launch into a tirade against the ref in question. Because obviously refs make mistakes out of a lack of respect, not because they’re just human like the rest of us. If refs respected managers they’d be perfect, just like them.
Oh, and to answer the question you forgot to ask: no, you should not support Manchester United. 
So you moved to England, eh? Seriously though, the euros do a lot more arguing and such after a call, than say the Asians or the Latinos, where the refs tend to be quicker to pull a card. Meaning the ref can give you a yellow card for being disrespectful to him.
I once got a yellow after a ref made a call against me cause I threw my arms up in a sorta “the fuck you mean that was a FOUL?!” gesture 
ETA: oh yea, and supporting Man U is basically the equivalent of supporting the Yankees, to put it in terms we Americans understand 
A colourful little theory; if only the facts bore it out?
Sour grapes! Man U haters are just full of sour grapes.
Man U has the annoying habit of winning, a lot. Seems to really piss people off.
I’m not sure the intricacies of soccer, but in rugby, part of the reason is because the referee is in charge of everything. He’s got a couple of touch judges, and (depending on the level) an assistant that takes care of substitutions and some up in the booth to help determine if a try was actually touched down or not. Another reason, and I don’t know if it holds true in soccer, too, but the time doesn’t end when we reach eighty minutes. The half or game does not end until the ball is dead. Going into touch, the offensive team creating a foul, or scoring a point are three ways to make the ball dead.
My first thought is that you’d need a way of indicating, without delay, whether a ball has crossed a touchline. This means a fairly significant change to the way the game is refereed, when the majority of fans and players are basically happy with the way it works at present, albeit the various minor gripes.
It’s pretty much the same for soccer, with the important principle that all games at all levels are adjudicated in the same manner, making technological solutions a difficulty.
Generally the referee will end the match when neither team has a chance to score a last-second goal, and normally when the ball is high in the air, preventing any controversy along the lines of ‘did it cross the line before the whistle?’.
But, to enlarge on this answer, the ball does not have to be dead for the game to end. (It does in Rugby League as well as Union, and in League traditionally an off-field hooter sounds “Time’s up”, but the game doesn’t end until the on-field referee blows up.)
In the NBA, the refs use special whistles with a little wireless transmitter built-in. When the whistle is blown the clock stops instantly.
American soccer actually tried to use an “official” countdown clock for a while in the 90s. I remember having to operate such a clock when working for the then second division California Jaguars in about '96. If the referee wanted the time stopped, such as for injury, substitution, etc., he crossed his arm above his head. When he blew the whistle again, the clock started.
Referees hated it. Why? Because they are uniformly a bunch of control freaks and didn’t like having this rule for the professional game, when every other match they officiated they kept the time on their super-secret wrist watch. That allows them to stop the game when they damn please, usually while the ball is in some neutral part of the field. (please note: I referee soccer, so I accuse myself with this particular paragraph, and the bit about “control freak” definitely applies! 
).
One of the main reasons it’s done the way it is is that soccer has tried to keep its rules and methods uniform from top to bottom of skill level. Referees in the Premier League in England are doing essentially the same thing that referees on the kid fields of America are doing, or on the lower level fields of Nigeria, or on the amateur fields of Brazil. This uniformity is starting to crack; certainly the Under-10 referee in America isn’t using a fancy microphone and headset setup to talk to his assisstants on the touchline. I think the final nail in the coffin will be when they go to goal-line cameras or whatever other technology they decide upon to determine if a goal has been scored. At that point, it will be “Katie bar the door” and we will see many improvements to the professional game, including a truly fair clock, kept OFF the field.
Excerpted from Law VII, FIFA Laws of the Game:
The ref blows for time when his watch indicates the end of the match - even if a player has fired a shot that crosses the goal line half a second later.
The only case in which the game continues past the time allotted (including time added on for stoppages) is if a penalty has been awarded. The duration of the half is extended “until the penalty kick is completed.”
The clock stops when the ball goes into touch?
Thanks for the other clarifications. Although I’m curious now as to the actual rule of when the game ends, since MHaye has posted a dissenting opinion.
Actually, I never said we moved to England. I said we moved from the U.S., and there’s a great deal of soccer on TV. We moved to Israel. There are always four soccer matches on at any given time.
Had you thrown them up in a “you mean that was a foul? 
” gesture, you probably would have just gotten a talking to.
It’s not the fact that they win that makes other soccer fans dislike them.
It’s any number of things, one of which is that arrogant sod Ferguson who seems to think he’s a law unto himself.
He can’t even lose with grace, he’s always got some excuse
Indeed I recall when I was a lad that very thing happened to Roy Race of Melchester Rovers although it may have been on the stroke of half time.