What is a better way to catch offsides with no linesman ? I'm not in the state that I can be beating the ball up the pitch getting into a position to see the offside AND being in a position to referee the game correctly (i dont know anyone who is) ?
With offside it is a guessing game, but the best thing you can do is drift wide. Let's say play moves down to the wing, if you drift wide to the wing as well so that you're in a position to watch the play but also look down/across the line on offside, then you're in a good position. You will never get a linesman's view of the offside though, and so, you're never going to get them right using this method either, but it's better than trying to do it in a central position. (You need to be fit, but this is also a good way to get fit!
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In games where the play is directing you central - i.e. teams that pass short and across the middle all the time, then things get trickier. For me, you need to identify when they'll pass a wide ball so you can get out wide again, but in those cases I sacrifice offside for keeping up with play and foul detection - these are more important and sometimes you need to drop further back in case the passing goes wrong and a counter attack starts.
Other things that will help you is identifying patterns of play and the team's tactical set up. If you can identify they're punting the ball long and central to a striker all the time, then check out his off the ball positioning every once in a while. You'll often see if they're making any effort to drop behind the line to make their run or if they're lazy and standing miles offside hoping you don't notice. Also, look at the defending team's backline once in a while. Sometimes you'll see a brilliant offside trap played by the centre-backs only for the right back (it's always the right back) to be sitting ten yards back playing everyone onside. If you see this happening, then anytime there's an offside shout, you know you need to find that right back so you can point at him and say he's playing everyone on.
Little things like that will help. But, as you said it's your first game, I think your priority should be keeping up with play and foul detection first. When you get comfortable with that, then you can start expanding on thinking about offside, player positioning etc. Put this way, if you're not giving any or many offside, most teams will adapt and play a low-block defensive line as they know they won't get anything from you. On the other hand, you don't want teams shifting up to nasty tackles because you're missing fouls. If that makes sense?
I also heard one player, again unknown shouting homophobic slur, not directed at anyone but in general. It was "f*****g f****t" on more than one occasion, how would you deal with this in the actual game not knowing who it is ?
I'd talk to the captain/manager. I'd also report it to the FA.