LIKE so many footballers, David Prutton is a different person when he crosses that white line.
Thoughtful, intelligent and placid off the pitch, he is always hugely determined, committed and psyched up on it.
Few Premiership players are so passionate - but fewer still have behaved more recklessly than the Saints midfielder on Saturday.
No one takes pleasure in heaping criticism on Prutton, but his behaviour on Saturday during a crazed ten-minute spell just before half-time leaves no option.
He let himself down badly and it was sad to see.
The two tackles that added up to his dismissal were both dreadful and each could justifiably have warranted a straight red card.
The first was a wild lunge on Mathieu Flamini, which fortunately did not do any damage to the young Frenchman.
The second was a late, scything challenge on Robert Pires. The ball had gone and slow-motion replays graphically showed the French winger's ankle buckle.
You could be generous and say it was mistimed. What wasn't in doubt, however, was that it was late and dangerous.
There could be no dispute about the sending-off which followed. Perhaps Prutton was furious at himself for such a potentially costly challenge for his team?
Whatever, the red card was like a red rag and he chose to express his anger at linesman Paul Norman, who had correctly advised referee Alan Wiley over the tackle.
Amid some pushing and shoving, what was perhaps most disappointing was Prutton's initial disinterest in the well-being of Pires in preference for shouting at the officials.
The ramifications of the incident look likely to be far-reaching.
Most frustrating for Saints was the fact that if Prutton had only accepted his dismissal, he could have been counting his blessings having got away with just a one-match ban for two very bad tackles.
As it is, you would have to guess he will be out for somewhere between four and ten matches.
One hopes he will now return to the team having addressed a discipline issue that has been bubbling away and threatening to erupt throughout much of his career.
He is only 23 and there is plenty of time to put Saturday behind him and become a better player for it.
For Saints, Prutton's reaction to his dismissal overshadowed another encouraging performance, as well as two equally bad challenges from Arsenal's Robin Van Persie.
Certainly, while both teams had 11 men and then ten men, Saints competed extremely well with the champions as they extended an unbeaten record at St Mary's to 14 games.
Boss Redknapp had encouraged his team not to show Arsenal too much respect in the build-up to the match and, spearheaded by Peter Crouch and Henri Camara, Saints enjoyed good early possession.
Camara's pace was causing Pascal Cygan difficulties and he skipped past the Frenchman before being tripped just a few feet outside of the area.
Linesman Norman waved his flag but Wiley shook his head as play continued to the outrage of most of St Mary's.
It was an open, entertaining match and the tackles were flying in, while both goalkeepers were forced to make comfortable saves.
The first card came on 30 minutes when Van Persie checked across Rory Delap and connected with an elbow to the face of the Saints right-back.
It could have been a straight red.
Prutton's two-part dismissal dominated the next few minutes and Arsenal quickly made their numerical advantage count.
Thierry Henry collected the ball in the Saints penalty area and found Freddie Ljungberg in space for an easy finish.
It looked like a lost cause at half-time, but the match was to turn back in Saints' favour following two crucial incidents in the space of just three minutes.
Van Persie had found an unmarked Henry just six yards out and a goal looked inevitable.
But Paul Smith brilliantly readjusted to block with his outstretched leg.
Moments later Van Persie went in recklessly on Le Saux, leaving Wiley with little alternative but to issue a second red card.
Crouch then made Arsenal pay.
Jamie Redknapp, who with Nigel Quashie had again been excellent in midfield, floated over a corner which Arsenal goalkeeper Jens Lehmann came to collect but completely missed.
Crouch rose highest and cleverly headed it into the ground between Ljungberg and Ashley Cole to make it 1-1.
The in-form forward almost then put Saints ahead on 70 minutes when he shook off Cygan but side-footed agonisingly wide.
At the other end, Saints had an inspired Smith to thank for a string of superb saves to stop Ljungberg, Henry and Cole.
The best of them denied Cole, who had surged clear and fired just to Smith's left only to be denied by an excellent block.
The England left-back did finally beat Smith in the 94th minute but his effort was correctly disallowed for offside.
Saints had shown great spirit. They deserved a share of the spoils and could be grateful that, in the words of boss Redknapp, Arsenal had a player who had been as stupid as Prutton.
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