We all make judgement calls and we all use selective enforcement of the rules. A batter says something and we ignore it because he is mad at himself. A runner takes his helmet off in relaxed play and re ignore it. I was always taught to know the letter of the law and to enforce the rules as fairly as possible. "If in my judgement, the runner made contact to hurt the fielder or to try to break up a play, I would have called interference!" I call obstruction and interference more often than anyone in my assoc. I study the BRD, the J/R, the individual rule books and use the forums. I don't claim to know it all and I still make mistakes.