Ref Watch: Costa, Lucas, Mertesacker - Dermot Gallagher's review

It was another weekend of controversial calls in English football, with Chelsea forward Diego Costa once again at the centre of a contentious decision.

Liverpool duo Martin Skrtel and Lucas were also involved in some key moments at Stamford Bridge, but should they have seen red? 

Swansea and West Brom were denied spot kicks which may have given them better results against Arsenal and Leicester, but should they have been given? 

Former referee Dermot Gallagher joined Rob Wotton on Monday's Sky Sports Now to look back over the controversial calls and discuss whether they were correct or not.

INCIDENT: Diego Costa (Chelsea) kicks out at Martin Skrtel (Liverpool)

SCENARIO: Diego Costa goes down under the challenge of Martin Skrtel inside the centre circle. Both men fall to the ground, with Costa making an unnatural movement with his right foot towards Skrtel and connecting with the defender's chest. 

GALLAGHER'S VIEW: Right decision

GALLAGHER SAYS: The minute they come together, Mark has rushed towards the incident. That is the key issue, he has seen the incident and dealt with it on the day, albeit just to speak to both parties. I think the fact that the players have settled it very quickly has helped. It was petulant and petty.  

INCIDENT: Martin Skrtel (Liverpool) elbow on Diego Costa (Chelsea)

SCENARIO: Diego Costa chases down a ball played down the left flank and is followed by Martin Skrtel. The Chelsea forward attempts to keep the ball in the play, but is closely followed by the Liverpool defender and is forced into touch. Skrtel appears to use his elbow to force Costa out of play, however referee Mark Clattenburg awards no foul and gives a goal-kick to Liverpool.

GALLAGHER'S VIEW: Right decision.

GALLAGHER SAYS: I don't think he's elbowed him in the face. Mark Clattenburg probably thinks it's a coming together. I think his elbow does come out, but to fend him off. We see all the time players fending one another off, that's what Mark has seen. In fairness, Costa does great as he does not get involved or make a big issue of it. 

INCIDENT: Lucas (Liverpool) tackle on Ramires, no second yellow card given. 

SCENARIO: Lucas, having already been booked for a first-half challenge on John Obi Mikel, brings down Ramires near the half-way line, halting a potential Chelsea attack. Referee Mark Clattenburg awards Chelsea a free-kick, but does not produce a second yellow card and subsequent red card to Lucas.  

GALLAGHER VIEW: Right decision

GALLAGHER SAYS: To get a yellow card, it must be reckless or deliberately breaking up play or an attack. But I think this is not a yellow card, I think it's a foul. Ramires, if he gets past Lucas, is head on to another Liverpool player. One of the worst expectations at the moment is the minute a player has a yellow card, the next challenge is worthy of a red card. Fouls are fouls in isolation. I don't think that was a red card. 

INCIDENT: Per Mertesacker (Arsenal) handles the ball in the penalty box against Swansea. No penalty given. 

SCENARIO: Swansea are awarded a free-kick 20-yards from goal. Gylfi Sigurdsson steps up and hits his effort towards goal, which is blocked away by Arsenal defender Per Mertesacker. The Germany international appears to make an unnatural movement with his arm towards the ball and makes the block inside the 18-yard box. Referee Kevin Friend allows play to continue without giving Swansea a penalty. 

GALLAGHER'S VIEW: Wrong decision

GALLAGHER SAYS: It's a penalty, there's no doubt about it whatsoever. One of the amazing things about this incident is the referee puts the wall back 10 yards, puts the spray line down and you always seen them saying "keep your hands down". The referee's view is absolutely perfect. Mertesacker deliberately puts his arm up and handles the ball away. It's a penalty, it cannot be denied. 

INCIDENT: Laurent Koscielny (Arsenal) goal against Swansea, goal awarded.  

SCENARIO: Mesut Ozil's cross is headed back towards his own goal by Swansea defender Ashley Williams. The ball loops up into the air, Laurent Koscielny back peddles towards Swansea goalkeeper Lukasz Fabianski, who attempts to make a claim under pressure from Koscielny and Olivier Giroud. Fabianski drops the ball, referee Kevin Friend allows play to continue and Koscielny makes no mistake, sweeping his effort into the back of the net. 

GALLAGHER'S VIEW: Right decision

GALLAGHER SAYS: I think it's a fair goal. The goalkeeper has come to punch and Giroud has every right to stand his ground, which he has done. I don't think there's enough there to give a foul. I don't think the goalkeeper has any intention other than to punch the ball. So I think it's a fair goal. 

INCIDENT: Jonny Evans (West Brom) penalty appeal against Leicester, no penalty given. 

SCENARIO: A West Brom corner is delivered into the 18-yard box. Jonny Evans gets across his marker, Leonardo Ulloa, before being hauled down as he attempts to connect with the cross. Referee Anthony Taylor does not award West Brom a penalty and signals a goal kick for Leicester. 

GALLAGHER'S VIEW: Wrong decision.

GALLAGHER SAYS: All I can think is that Leicester's number nine goes across his line of sight. Without a doubt, he has pulled his shirt so far that it has to be a penalty. That is the only reason I can think that the penalty was not given. 

INCIDENT: Darren Fletcher (West Brom) penalty appeal against Leicester, no penalty given. 

SCENARIO: James McClean crosses the ball into the 18-yard box, which is met by Darren Fletcher. The West Brom midfielder controls the ball on his chest before being challenged by Leicester defender Robert Huth. Fletcher falls to the ground, with referee Anthony Taylor waving play on. 

GALLAGHER'S VIEW: Right decision

GALLAGHER SAYS: I am not really convinced by this to be honest. I don't think this is a penalty and the reason I don't think it is, is that they both go up and it's a coming together. 

INCIDENT: Riyad Mahrez (Leicester) goal against West Brom, goal given. 

SCENARIO: Mark Albrighton's cross deflects off a West Brom player and into the path of Riyad Mahrez. The Leicester winger, standing in an offside position when the initial ball was played, produces a volleyed finish past Boaz Myhill. The linesman on the right side keeps his flag down and the goal stands. 

GALLAGHER'S VIEW: Wrong decision

GALLAGHER SAYS: It should have been definitely ruled out. The key issue is the start position of the player, he is clearly ahead of play. The assistant referee has not spotted it. It does strike the West Brom player on the way through, but that is a red herring, as the player must deliberately play the ball which he has not done. 

INCIDENT: Victor Wanyama (Southampton) sent off against Bournemouth. 

SCENARIO: Wanyama, booked in the first-half for a late tackle on Bournemouth defender Adam Smith, receives his marching orders after bringing down Lee Tomlin late in the second-half. Tomlin moves towards the 18-yard box, evading two challenges before being brought down by Wanyama. Referee Craig Pawson awards Bournemouth a free-kick and shows Wanyama a second yellow card and subsequent red card. 

GALLAGHER'S VIEW: Right decision

GALLAGHER SAYS: I think this is the best referring performance of the weekend. The first challenge is definitely a yellow card. He has gone to ground, he is late and reckless. The second yellow card, the Bournemouth player is on the edge of the 18-yard box and he is breaking up a promising attack. It's a foul and it's a yellow card.