Six Nations Championship: The shadows cast by Donncha O'Callaghan on an international pitch are usually unrestrained and foreboding. It's partly the job, partly the man. The intense eyes and the mop of long, dark hair licking around his face are that of the marauder going around the pitch hitting, running, clearing, pulling, tackling.

For the secondrow, it is fitting enough as the O'Callaghan clan motto is "Faithful and bold", while the O'Callaghan surname is derived from the Gaelic Ó Ceallacháin, which comes from ceallach, meaning strife or contention. O'Callaghan is a giver of strife, a purveyor of contention. How perfect.

Furthermore, the most notorious of the Callaghan clan from Cork was one Donncha, chief from 1537 until his undeservedly peaceful death in 1578. During his career, Donncha was reputed to have carried out 200 cattle raids in every county of Munster.

Wales should really get to hear of this rich and outlaw-like ancestry and although O'Callaghan understands he is included this week because of injury to Paul O'Connell, the lock is at peace for the moment. He has been around too long to not understand the dynamics of three big players wanting to squeeze into where only two can fit. For this Celtic battle O'Callaghan is genetically very well set up.

"Competition is brilliant because you can't afford to play bad and you can't afford to rest on your laurels," he says. "You have to be playing well. Through injury and given a chance on Sunday I'll just be looking to perform.

"We've always had the opinion within the squad, the secondrows, that the two men who are lucky to go in under pressure know that the man sitting on the bench is really breathing down their necks. So there comes an awful lot of pressure when you're given your chance and you have to take it."

It is an illustration of that competition that O'Callaghan has already won 22 Irish caps but continues to be steeped in a never-ending battle with the world class O'Connell and Malcolm O'Kelly. He doesn't expect to dispossess O'Connell but he can play well enough to cause Eddie O'Sullivan serious selection headaches.

"When you get your chance you want to perform in front of the coaches," he says. "But for me it's the respect of the players and knowing that I can look around the dressingroom afterwards and know I have not let any one down.

"Everyone has to perform. Paul O'Connell has set the standard for secondrows in this country. People are quite aware that he's something special. When I've chatted about Paul, I've never tried to put myself in the same bracket as him because I think it would be disrespectful. He's a world-class player and will be a big loss to us come Sunday."

The confusion in Wales and the threatened legal action from former coach Mike Ruddock combined with the loss of captain Gareth Thomas has been subjected to various analyses. No one knows how the team will react but from O'Callaghan's experience of the Munster mentality and their ability to bind more forcefully around issues that might weaken other teams, a down-at-heel Wales represents a considerable threat.

"It can work two ways: it can galvanise a squad as well. You know when you are pinned into a corner you can gel together and push on for each other. From knowing a few of the Welsh lads they are not the types to sit around and moan and groan. They get on with things. Certainly it was a disappointment to lose Mike Ruddock. He was a good man in any dealing we had with him. The squad he's left there are good enough to go on. The players have to step up now and they'll have no problem doing that."

The tough attitude is apparent with the bold, faithful O'Callaghan. Seasoned now, even a swipe at the rest of the team is not out of the question. This week is about being more self-critical and less sympathetic to their own team lapses.

"Everyone knew that the start (against France) wasn't great and a lot of things didn't go our way," he says. "That's been the case for a few games. We've made errors ourselves. That's all well and good, the unforced errors, but you have to stop it at some stage.

"I think we have to get tougher on each other in terms of not accepting those kinds of thing. We've got to set a higher standard and that's been the case all week in training. Fellas have piped up when things are going well or when things aren't. Hopefully that will carry through."