He said:"Sometimes players have to take responsibility and i asked them why their season has gone like it has. Bryan Robson left some good players behind and it can be too easy just to blame a manager when results keep going against you.
"Its time we just stopped talking about the problems and messing about because it has been going on for too long. Players have to show they have the balls to play for this Club and i am questioning some of them if they have the courage to play at Bramall Lane."
Blackwell also expressed out that their will have to be changes.
He said:"If they can't handle it, i will find out who just can, so players futures at this club are under threat and if things dont improve over the next couple of games there will have to be changes.
"Lad on the Kop can see it wasn't good enough and they are the ones who work all week, pay to watch us and would give up a weeks wage just to get the chance to play for Sheffield United."
Blackwell finished:"I was embarrassed and to be fair i think the players are too. If they are not, they will find out pretty soon that they should be. The fans were great because they could have turned against the team as they have done on occasions in the past."