You would typically abandon the game for one of 4 main reasons
1) change in external conditions - e.g. A massive downpour that has flooded the pitch, or at an evening game a floodlight failure
2) one team fallls below the required number of players to continue, this could b due to misconduct, player injuries or a combination of the 2
3) a severe injury to a player, for example a broken leg
4)misconduct that has led you to decide it's not safe to carry on. This could include a mass brawl or an assault or threat of assault on you or other match officials.
The most important thing is to make sure both teams know what is happening and why you are doing it. Whether you want to go and stand in the centre circle and blow your whistle is up to you
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The one thing I would say is that if you make the decision to abandon, you should not make any comments or promises about the outcome of the game. Teams will often try to get you to 'award' them the game. You need to be clear that your job is to advise the league of the reason for the abandonment, the time of it and what the score was at the time and emphasise that it's down to the league to decide on the outcome. That's the most important thing you can do.