Most teams and coaches play with a set formation. What I meant by that is, if a team plays with a 4-3-3, they usually stick to that formation whether they are attacking or defending. Sometimes they will alter that formation in the latter part of a game if they are losing and need to attack more, or if they are winning and need to hold on to a lead. But these are usually desperation measures hoping to salvage something from a game and not their typical way of playing.
When I coached my teams to state championships and a National Championship, my teams would always have a different line up when attacking and when defending. This depended on the team, and players available for that team as to how those formations were structured.
But I am happy to see that this flexibility in formations during games is now becoming more prevalent with Jurgen Klopp at Liverpool as a classic example. His ideal formation is the 4-2-3-1, but because of the players he has at Liverpool, he tends to play more with the 4-3-3 when in possession of the ball. He still uses the 4-2-3-1 a lot when doing his famous high pressing the opposition. But the bottom line is, he is flexible in this and doesn’t stick to a rigid formation throughout the game.
When my 87G Dynamos won the National Championship, I used a 4-4-2 when defending, but this changed to a very aggressive 2-4-4 when attacking.
I was able to use this aggressive system of play because of the speed and athleticism of the players as well as our superior conditioning, which I go into more detail in my book.
The reason we played with this formation was probably because I’m from England and that is what I played and coached back in the day, and what I was most comfortable with. I did use the 4-3-3 and 3-5-2 formations with some of my other teams depending on the players available, but for this team I used very aggressive 4-4-2 formation that was fluid enough to move to a 4-3-3 when needed.
For a more detailed look at this and information on how I adjusted our style of play that gave us an edge in every game, check out my book, Coaching a Team to a National Championship.