Thanks for the playthrough :). To confirm for you, swapping the jerseys went good. Never swap jerseys unless a card says you can do. So you begin with 5 attacking players and 5 defending players. After buying players or training youngsters then you swap the number if you need to. So number 4 came back as defender is correct. Few things what went wrong are with the tactic cards. You start with 1 random tactic card which have 2 formations on it. Later on you can gain tactic cards (with the director for example) like long passing and formation 5-4-1. In other words, you never start the game with an ability tactic card. After you read the scout report, you use one of your tactic cards for formation. After you revealed opponnent, you may use a different tactic card for his ability. You can't use 5-4-1 and the ability long passing together with this card, because you just may use 1 of them. And the ability long passing, you checked forward oponnent and own defender. You need to check your own assigned player card defender with your own assigned player card attacker. If your 2 players has the same strenght, they have a "connection" for the long pass and striker scores a goal.
as someone else commented, rules state that you have 5 offense and 5 defense players to start, and you cannot change this unless a specific card text allows it.
I think the concept of rolling the score for each non playing team, is that they are not playing each other. There are ghost teams in the league which they are playing against. It would have been better, though, to have an active league with a schedule and head to head for non playing teams.
