LONDON — West Ham captain Mark Noble grappled a pitch invader to the ground and the struggling English Premier League club's owners were forced to flee their seats to escape protests during a loss to Burnley on Saturday.

Lax security allowed two more fans to come on the field at the Olympic Stadium before being led away by West Ham defender James Collins.

Burnley forward Ashley Barnes also tripped another pitch invader, while a supporter was able to pick up the corner flag and plant it in the centre circle.

In addition to four separate pitch intrusions by supporters, police said they received two allegations of assault on an afternoon when frustrations about West Ham's plight boiled over.

As the English Football Association investigates the unrest, the Premier League separately said it would be contacting West Ham to seek assurances that the disorder would not be repeated at future matches. West Ham called an emergency meeting with the publicly owned stadium's operators and said it was "committed to taking decisive and appropriate action" against the perpetrators.

As West Ham scraps to stay in the Premier League, sitting three points above the relegation zone, resentment has grown over the decision to uproot from the Upton Park home of 112 years to Olympic Stadium in 2016.

Hundreds of fans congregated beneath the directors' box to chant "Sack the board," which includes co-owners David Gold and David Sullivan. Some supporters made a throat-slitting gesture while missiles were seen being thrown in the direction of the executive seats.

The first pitch invasion came moments after Ashley Barnes gave Burnley the lead in the 66th minute. A man ran onto the pitch from the home end. With no stewards on hand to remove the fan, an enraged Noble grabbed him and threw him to the floor.

After Chris Wood put Burnley 2-0 up, another fan picked up the corner flag, marched to the centre circle and planted it in the ground.

"There is no place at any level of the game for what happened at the London Stadium," the Premier League said. "While the official investigation of the incidents will be carried out by the Football Association, we will be asking our own questions of West Ham United about what happened this afternoon, especially to ensure similar events never reoccur."

It was a tumultuous end to a turbulent week that saw a protest march called off as West Ham fans groups turned on each other.

"What we need is the club, supporters, players, everyone, is to pull together," West Ham manager David Moyes said.

"All I ask for is that everybody sticks together and we try to get ourselves enough points to make sure we're a Premier League team (next season)," he added.

Many fans have never accepted watching their team in the stadium that was designed primarily for athletics at the 2012 Olympics.

Whereas Upton Park provided a formidable atmosphere, fans are separated from the pitch by the running track in their expansive, largely taxpayer-funded new home. It is only being rented from the company in charge of securing the legacy of venues from the 2012 Olympics.

The holding name "London Stadium" highlights the failure to secure the naming rights envisaged — a pursuit that could be even harder after the latest turmoil.

"An emergency meeting has been called with all London Stadium stakeholders," West Ham said.

The Football Association "strongly condemned" the crowd disturbances and said it would be seeking observations from West Ham.

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