I think your domain model is not correct. I assume that the skillset is a table with all the skills that players could possible have and the skillscore is the score of that particular player with that skill. Now a skill can only be coupled to one skillscore. This should be multiple (skillscore) to one relation (skillset). And assuming that a player has multiple skillsets you have a many to many relation between players and skillsets, because a skillset can belong to multiple players and each player has multiple skillsets.
If this is so you need the reference set selector so you can add skills to each player. And when editting the skillset you can then place the reference selector to define the skillscore.
And also take a look at your trainer - player relation. I think that a trainer has multiple players but a player probably has only one trainer, now you have also drawn a reference the other way around. Either make this then a multiple to multiple relation or remove this one.