Thanks for your reply. I will try your suggestion and turn some players to support duty. Do you think I should change the players roles? I basically want my team to play possession football and send in lots of crosses. So what do you think I should change in my tactics to make them better?
It's finding the right balance, I personally make sure I have at least 1 defend duty in midfield, mainly because I like to protect my back four. I would also have a support duty in one of those attacking 4 in a 4231 myself. You could probably find playing possession could really benefit from roles in certain ways, you also need to decide who you see making those crosses. If it is the wingers, then maybe you want them to have a role that aims to get crosses, if it is the full backs then maybe you want them to cut inside and be in the box for the crosses. If you o that you'll find the roles will practically pick themselves on how you want the team to play as a whole.
Short passing may be a worthwhile team instruction, but you may find you are acheiving that already with the right positions, roles and duties.
From my guess of the players you have and the way you want to play however I would probably be thinking something like this in the 4231 formation you use.
Mentality: Control/Counter this depends how you want to play, do you want to sit back and then attack forward quickly on the break? If so I'd probably guess Counter. Control would be more if you want to be looking to attack more, get the ball forward quickly. Or maybe you want neither and then Standard could be better.
Team Shape: Flexible (I personally always use this but this could be up to you, I find Rigid/Very Rigid restricts your players to play their role and not have any place for them to think for themselves, while fluid/very fluid I just avoid myself s I find the players don't do what I want, but from what I've read, that is more worthwhile using generic roles like CM, CD, Defensive Midfielder, Attacking Midfield etc.and not good with roles like DLP, BWM, False 9, Anchor Man etc.)
Team Instructions: N/A I personally wouldn't set any until the team is fluid in the tactic and you can spot things you feel the team are either doing too much or not enough as a whole (same goes to player instructions)
Now for the next part of players, this is where it gets a little bit tough as I don't know the players well but guessing by how you want to play, I'll take a crak
GK: Sweeper Keeper/Support (kept this as you had as I imagine you want to him sweeping up through balls)
LB: Full Back/Support (again kept this the same, I see him supporting the left winger but I picture him as being sensible with this)
CBL: Central Defender/Defend (again kept this the same, no harm in what he is)
CBR: Ball Playibg Defender/Defend (again kept this the same, but I'm hoping Pezzella has decent passing, decisions especially to know when to play the ball like this, if not I'd put him as the same as the other CB)
RB: Full Back/Attack (the reason I've gone for this is because I imagine he Darmian is actually a pretty good dribbler and crosser, so it makes you a bit more varied to the left)
CDML: CM/S or BBM/S (I imagine you see this guy as your legs in the middle, a jack of all trades type player, maybe get to the edge of the box now and then but also willing to run and track back to help the defence)
CDMR: DLP/D (if the other guy is on support I'd immediately want this guy on defend, he will be less forward as a result of this and offer some protection to your back 4, also he should hopefully be the first player your defence will look to as a passing outlet and he is the man to look to spray the passes to the main attacking 4)
AML: Winger/Attack (as said above, I'm guessing this guy is more of a winger than the AMR, although I don't know that much about him, someone to get to the byline and deliver crosses as much as he can, while he has a full back behind him at all times to keep the defensive numbers up)
AMR: Inside Forward/Support (this is a tough one, I'm guessing you want him to cut inside and have shots at goal, but I've never really used an Inside Forward on Support duty so he may be more suited to the Attack duty, but I wouldn't want all 3 attacking mid's on Attack myself)
AMC: AM/A or AP/A or SS/A (these 3 all spring to mind but it depends on exactly what you want him to do. A mixture of goals and assists, then AM/A could be more suited as he will have a few pops at goal but also look to pass as well. Primary assists, then maybe AP/A, more likely to hover around the edge of the area and look for the AMR/ST in the box or get the ball out to your winger/RB for a cross. Shadow Striker if you want him to get in that box and score as many goals as possible, but aren't concerned on him being very defensive)
ST: CF/A or AF/A (I don't think El Shaarawy is much of a hold up player from what I know about him, I thought he played out wide most of the time but again my knowledge of him isn't great, so I think a duty of Complete Forward could be slightly risky as it expects them to do as many of the Striker roles in one, look to hold up the ball and pass it, keep the ball and dribble past people to score, or get into the box and be the main person players are looking for. Advanced Forward from what I remember is basically the pin point of your attack, he will get in the box and look to score as often as possible, but still maybe try to feed the Inside Forward and the Winger or maybe even the AMC if he is a Shadow Striker)
This is all a guess however without knowing the players, but that's why I've given my thinking behind it in brackets. It also depends on how you want to play. Maybe do what I've done and post what you want each position to do/what role/duty you feel is best for them and everyone would happily assist you in that way, trust me as I've asked questions loads of times.