Sergio Busquets ended the Clasico frustrated after a key penalty decision went against Barcelona in the 3-1 loss to Real Madrid.
A spot-kick was awarded at 1-1 when Sergio Ramos and Clement Lenglet came together in the box in the 63rd minute.
"We were really looking forward to this game, I think we went into it well despite losing last week to Getafe," Busquets told Barça TV.
"It was an even game, especially in the first half. We were better at the start of the second half and there were some dangerous moments, especially the Coutinho chance, which was quite clear.
"But after the penalty, the balance tipped in their favour. They were much more comfortable, sat deep and came at us on the counter-attack."
On the criteria for VAR, Busquets added: "It's difficult, as the coach said. You see games and a lot of plays like that (Lenglet and Ramos). There was one much clearer which Real Betis don't get the other day.
"Sometimes VAR steps in, sometimes it doesn't. They say it has to be really clear and I think today's one was too much of a punishment."