Former Scotland striker Ally McCoist was baffled by something one Arsenal star did in the first half against Chelsea on Tuesday evening. Arsenal got off to a flying start when they welcomed Chelsea to the Emirates Stadium. The Gunners knew that they needed to win this match in order to extend their lead at the top of the Premier League table, and Leandro Trossard duly fired them ahead from a tight angle with just four minutes on the clock. However, with the Blues posing a real threat on the counter-attack, Mikel Arteta will have wanted to see his side build on their lead as ruthlessly as possi…