This Trophy will pop when you reach max Coach Level (20). To level up you need to accumulate XP from playing official NAF Online League or Solo League matches. Each Match will earn you 10 XP with a bonus of +3 for a Win and +1 for a Draw. You will need to accrue a total of 706 XP to hit Coach level 20. This is gonna take a while, since you will need to play a between 55 and 71 Online or Solo League matches to hit 706 XP.
You'll need to play quite a few matches to get some of the other Trophies so, sit back and enjoy some Blood Bowl!!!