Liverpool fans have every right to feel frustrated by Manchester City's 3-1 victory over Watford on Saturday.

Raheem Sterling's hat-trick moved City four points clear at the top of the Premier League to put all the pressure back on Liverpool, who host Burnley on Sunday.

But there were big question marks about Sterling's opening goal in the 46th minute.

With the game at 0-0, Sergio Aguero tee'd up his English teammate only for Daryl Janmaat's clearance to ricochet off him into the back of the net.

The linesman raised his flag for offside, but referee Paul Tierney overruled the decision. Replays showed Sterling was in an offside position when Aguero chested down the ball.

There was immediate confusion about why the goal was allowed to stand and it was suggested that Sterling wasn't active until Janmaat tried to clear the ball away.

But the counter argument was that Janmaat only tried to clear the ball because of Sterling's presence, which meant he was active.

Law 11.2 in the International Football Association Board's rule book states that:

"A player in an offside position at the moment a ball is played or touched by a teammate is only penalised on becoming in active play by clearly attempting to play a ball which is close to him when this action impacts on an opponent."

The laws on offside certainly seem to suggest that Sterling was offside and now former Premier League referee Chris Foy has backed up that notion.

"Raheem Sterling's first goal should have bee ruled out for offside," Foy explained, per the Daily Mail. "A player in an offside position at the moment the ball is played by a teammate is penalised if he clearly attempts to challenge for the ball.

"Sterling was in an offside position when Sergio Aguero flicked the ball on. Even though Daryl Janmaat got a touch before the ball reached Sterling, the City winger had clearly attempted to play it as well.

"This action affected his opponent, so it is offside. It is a difficult decision as there are many things for the officials to consider. I think they saw the Watford defender play the ball onto Sterling but not that he also challenged for it as well."

So there you have it, Sterling's goal shouldn't have stood and the referee made a big mistake. Over to you, Liverpool.