you can't change tactics in the middle of the season, all you will do is destabilize the team.
Furthermore, there is a specific tactic and playing style for each team you face. Defence+swift counter-attacks with wing-play when playing strong teams, attacking, posession and no wingers against weaker teams and variations of these: some teams use a dangerous AMC who can turn into a ST in no time, thus you need to play a DM to anchor him down, teams with no wingers can be exploited by fully utilising wing-play and narrower width and so on. There is no best tactic as some describe theirs, it's what suits your team when playing against another side with a specific layout on the field. So try to think it out and make your own tactics before games, don't just copy some "super tactic" you find on the net, made by someone who probably knows less about you about the game. | 
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