Denis Betts aired his frustrations after Widnes lost their fourth consecutive match.
Despite taking an early lead, the Vikings fell short against Castleford, who recorded back-to-back wins in this 34-24 triumph.
Among several criticisms, Betts was unimpressed by his side’s defence.
“Defensively we were slack from the start,” he said.
“We just didn’t control the ruck right through to the end of their sets. After the first five or 10 minutes we just went a little bit soft on ourselves. We were 12-0 up but I was still seeing things in us that weren’t strong. There was a bit of ill-discipline and areas of our game where we gave them field position too easily.
“They had nothing to lose and they came back. It was a massively disappointing day. We get 18 points up and Joe Mellor gets away down the sideline but effectively bombs a try.”
An exclusive interview with Chris Dean plus a full-page report of the match is in the new League Express, available in stores now or online here.