He doesn't look to see where the ball is and leads with his arm .
DC what are you on about ? this is your gawd knows how manyeth post justifying the sending off, and you are still wrong. Of course you are going to look and see where your opponent is before you jump to challenge him for a header - there's no point in challenging otherwise. You can even check again if you have time. If you can see where the ball has been passed from (or in this case lumped up the park from) as a professional you should be able to judge the flight of it, and where you/ opponent and ball intersect. Tansey did. As for your "interpretation" of the laws of the game, they are just that - laws. There is no interpretation. Law 12 (fouls & misconduct) lays them out perfectly well. The referee can only send Tansey off for either "serious foul play" or "violent conduct" There is no such offence as "leading with the arm" I can see no evidence of either of these offences in the highlights. He could only caution Tansey for "unsporting behaviour" which again there is no evidence of. He could have awarded a direct free kick for any number of described offences, including "jumps at an opponent" in a manner that the referee considers "careless, reckless or using excessive force" That is the offence that you have described, and that is the proper outcome according to the Laws of the Game. As my dad would say "gie's peace", but I won't hold my breath for you having the good grace to change your mind.
When have I said there was an offence of leading with the arm ? Violent conduct pure and simple .