The assaults on Martina are way over the top. He's not the greatest defender but Coleman wasn't exactly a maestro in that area either. He gets forward and does his job, puts good crosses in. He's doing better than Baines this season and doesn't deserve the criticism when the entire team is performing well below par.
Coleman was shaky defensively when he first came which is why moyes played him right wing rather than have him exposed at full back. However since about December 2012 he has been pretty flawless defensively, cant think of a major fault he has defending and very rarely makes costly mistakes in that time. Martina's level of defending cant be compared in any way to Coleman, you are talking about someone who is and has been one of the most complete right backs in the league for 5 years against someone who lets be honest isnt on our level, or where we should be.
He isnt poor all the time, he was ok yesterday. However his poor moments are of a really bad level and some of the things he does are just really poor in comparison to Baines playing badly he isnt making many mistakes he just isnt doing what we got used to him doing. Defence in any area is a hard position to put up with someone who is inconsistent and range from looking generally ok at most things to doing things like that clearance at home to Spurs last week for the second goal, or the header a few minutes after where he cushioned it down to Kane inside the box. He defends crosses with his back to the play, he has a really poor timing of a leap defensively, he can be easily beaten one on one and he has as we have seen bad errors in him.
As i said it isnt all the time he could be fine on Wednesday then awful on Saturday and cost goals. It's hard to play a defender who has that inconsistency in them because the poor moments cost you goals. If Seamus was fit and playing pretty much every game it wouldnt be a massive issue but because Holgate lacks so much going forward at right back and Martina is playing a lot of games his flaws are being highlighted. It isnt all his fault but he isnt a good right back.