I think there are a number of factors with the main one being fitness. I'm not sure what the plan was pre-season but not many of the actual first team seemed to be as fit as they should be when the season started.
Jags was injured at the tail end of last season and then had a bad time at the World Cup mentally. Distin seems to be suffering with injuries as well. But it's not just them, McCarthy doesn't look the player he was last season and neither does Barry. McCarthy lost his man 3 times against Chelsea. Against Arsenal Jags looked out on his feet. Basic fitness should never be an issue at this level.
Everyone knows from their own experiences when you are tired physically, you don't think as quick and I think that has been the problem. Slow in body, slow in mind and players are getting caught out and making mistakes they wouldn't normally make. Once that uncertainty creeps in, then confidence goes, and suddenly no one looks comfortable.
The worrying thing for me is that last season we had loads of soft tissue injuries throughout the season, which can occur when fitness is not at a premium. it's not bad luck that 5 or 6 different players all had hamstring issues. I wonder how they monitor fitness levels and if the players are as fit as they have been in the past.
To add to all that, Martinez system much like brenda and Wenger's, seems to have the full backs bombing on high up the pitch, leaving large areas of the pitch exposed. If your players then don't have the mobility to cover that ground, then you have the Kevin Keegan effect and need to score 3 goals to have a chance. We have also been playing with 2 almost out and out wide players, Mirallas has been working hard to try and add defensive duties to his game, but McGeady and Atsu clearly haven't. This leaves us even more exposed from a defensive standpoint.