private function persistPlayer($data){

    $player = new Player($data);  //Player __construct entity extracts + assigns data

    foreach ($data->skills as $rawSkill) {
                $skill = new Skill($rawSkill->ability);
                $player->addSkill($skill);
            }
    }

    $this->entityManager->persist($pokemon);

    try {

        $this->entityManager->flush();

    } catch (Exception $e) {

        error_log($e->getMessage());

    }
    return $player;
}

class Player
{
    /**
     * @ORMId()
     * @ORMGeneratedValue()
     * @ORMColumn(type="integer")
     */
    private $id;

    /**
     * @ORMManyToMany(targetEntity="AppEntitySkill", inversedBy="skill",cascade={"persist"})
     */
    private $skill;

   public function addSkill(Skill $skill): self
    {
        if (!$this->skill->contains($skill)) {
            $this->skill[] = $skill;
        }

        return $this;
    }

    //.... more code

}

/**
 * @ORMEntity(repositoryClass="AppRepositorySkillRepository")
 */
class Skill
{
    /**
     * @var integer $id
     * @ORMColumn(name="id", type="integer", nullable=false)
     * @ORMId
     */
    private $id;


    /**
     * @ORMManyToMany(targetEntity="AppEntityPlayer", mappedBy="skill" ,cascade={"persist"})
     */
    private $skill;


//...more code


}