A thrilling encounter at John Smith’s stadium featured four sin-binnings, with two players on each team being yellow carded.
Both coaches admitted those decisions had a major bearing on the game, which was decided by a Ricky Leutele hat-trick after Tigers had hit back from 18-0 down to lead 24-18,
Radford was encouraged by his side’s second half fightback, but admitted the poor start caused their downfall.
He said: “We went from major disappointment at half-time to thinking we were in with a chance, but ultimately, after that first 40 minutes, we shouldn’t have had a chance.
“We didn’t get right what we wanted to, particularly in our contact areas, but they don’t give in, they keep swinging.”
Giants coach Ian Watson was delighted with his team’s first half effort and the way they responded to going behind.
He said: “In the first half I thought we were as good as we were against Salford last week.
“In the second half we came out and we were a different team.
“Cas upped it and brought it to us, we dropped off things and put ourselves under pressure.
Watson felt the sin-binnings were “harsh.
He added: “You need to win the game the right way.
“We want the players to decide the game - you don’t want the game to be 12 versus 11.
“At the moment we are getting a lot of sin-binnings.
“We are talking about the wrong things, we need to be talking about the quality on show, someone like Ricky Leutele turning up and doing what he did at the end of the game to win it.”