At the club’s training base in Walsall, in the 40th minute of the friendly, the two were seen raising their hands and trading blows, with the score being goalless.
After being knocked down in the Mallorca half, Republic of Ireland midfielder Molumby, who missed the second part of the previous campaign due to a foot injury, responded when opposing number Costa approached him.
The visiting midfielder appeared to raise an arm when Molumby, 24, and 23-year-old Portuguese Costa engaged in a head-to-head match, but Albion’s midfielder responded with a blow of his own.
The referee then called an early break, five minutes before the half, as players from both teams rushed in to try to split the pair, who collapsed to the ground.
Manager Carlos Corberan substituted Molumby for the start of the second half. Costa seemed off as well. In the 65th minute, a free-kick from the six-yard box rebounded and was tapped in to give Mallorca the lead.
A Spanish broadcaster is providing live online streaming for the friendly.
