What is a "Professional Foul" these days?

I was under the impression that shirt tugs,sneaky obstruction,deliberate knock ons,throwing the ball away after a penalty award to the opposition came under the umbrella of professional fouls.
It has been argued on another thread that hitting someone late,high and with no use of the arms is a Professional Foul.Is this correct?
I must be more out of step with modern Rugby than I thought!

Taffineastbourne wrote:I was under the impression that shirt tugs,sneaky obstruction,deliberate knock ons,throwing the ball away after a penalty award to the opposition came under the umbrella of professional fouls.
It has been argued on another thread that hitting someone late,high and with no use of the arms is a Professional Foul.Is this correct?
I must be more out of step with modern Rugby than I thought!

Taff, a few years ago AWJ was rightly YC for a trip behind the refs back IIRC, in this years England v Ireland game in the RK try Poc pulled back I believe Joe Launchbury who was coming into the position to tackle RK, this try determined the winning of this years 6N.
England would have had 7 taken out of the against column and Ireland would have had 7 less in the for column.
When Poc was pulled back by Jonathon Thomas in an Ospreys v Munster game he absolutely poleaxed JT, at least JL restrained himself

LAW 10 : FOUL PLAY

Foul play

is anything a player does within the playing enclosure that is against the letter and spirit of the Laws of the Game. It includes obstruction, unfair play, repeated infringements, dangerous play and misconduct which is prejudicial to the Game.
Law 10.4 - Dangerous Play and Misconduct

(a) Punching or striking.

A player must not strike an opponent with the fist or arm, including the elbow, shoulder, head or knee(s).
Sanction: Penalty kick

(b) Stamping or trampling.

A player must not stamp or trample on an opponent.
Sanction: Penalty kick

(c) Kicking.

A player must not kick an opponent.
Sanction: Penalty kick

(d) Tripping.

A player must not trip an opponent with the leg or foot.
Sanction: Penalty kick

(e) Dangerous tackling.

A player must not tackle an opponent early, late or dangerously.
Sanction: Penalty kick

A player must not tackle (or try to tackle) an opponent above the line of the shoulders even if the tackle starts below the line of the shoulders. A tackle around the opponent’s neck or head is dangerous play.
Sanction: Penalty kick

A ‘stiff-arm tackle’ is dangerous play. A player makes a stiff-arm tackle when using a stiff-arm to strike an opponent.
Sanction: Penalty kick

Playing a player without the ball is dangerous play.
Sanction: Penalty kick

A player must not tackle an opponent whose feet are off the ground.
Sanction: Penalty kick

(f) Playing an opponent without the ball.

Except in a scrum, ruck or maul, a player must not hold, push or obstruct an opponent not carrying the ball.
Sanction: Penalty kick

(g) Dangerous charging.

A player must not charge or knock down an opponent carrying the ball without trying to grasp that player.
Sanction: Penalty kick

(h) A player must not charge into a ruck or maul. Charging includes any contact made without use of the arms, or without grasping a player.

(i) Tackling the jumper in the air.

A player must not tackle nor tap, push or pull the foot or feet of an opponent jumping for the ball in a lineout or in open play.
Sanction: Penalty kick

(j) Lifting a player from the ground and dropping or driving that player into the ground whilst that player’s feet are still off the ground such that the player’s head and/or upper body come into contact with the ground first is dangerous play.
Sanction: Penalty kick

(k) Dangerous play in a scrum, ruck or maul.

The front row of a scrum must not rush against its opponents.
Sanction: Penalty kick

Front row players must not intentionally lift opponents off their feet or force them upwards out of the scrum.
Sanction: Penalty kick

Players must not charge into a ruck or maul without binding onto a player in the ruck or maul.
Sanction: Penalty kick

Players must not intentionally collapse a scrum, ruck or maul.
Sanction: Penalty kick

(l) Retaliation.

A player must not retaliate. Even if an opponent is infringing the Laws, a player must not do anything that is dangerous to the opponent.
Sanction: Penalty kick

(m) Acts contrary to good sportsmanship.

A player must not do anything that is against the spirit of good sportsmanship in the playing enclosure.
Sanction: Penalty kick

(n) Misconduct while the ball is out of play.

A player, must not, while the ball is out of play, commit any misconduct, or obstruct or in any way interfere with an opponent.
Sanction: Penalty kick

(o) Late-charging the kicker.

A player must not intentionally charge or obstruct an opponent who has just kicked the ball.
Sanction: The non-offending team may choose to take the penalty kick either at the place of infringement, where the ball lands or or where it was next played.

Place of infringement. If the infringement takes place in the kicker’s in-goal, the penalty kick is taken 5 metres from the goal line in line with the place of infringement but at least 15 metres from the touchline.

The non-offending team may also choose to take the penalty where the ball lands or is next played before landing and at least 15 metres from the touchline.

Where the ball lands. If the ball lands in touch, the mark for the optional penalty kick is on the 15-metre line, in line with where it went into touch. If the ball lands, or is next played before landing, within 15 metres of the touchline, the mark is on the 15-metre line opposite where the ball landed or was played.

If the ball lands in the in-goal, in touch-in-goal, or on or over the dead ball line, the mark for the optional penalty kick is 5 metres from the goal line, in line with the place where the ball crossed the goal line and at least 15 metres from the touchline.

If the ball hits a goal post or crossbar, the optional penalty kick is awarded where the ball lands on the ground.

(p) Flying Wedge and Cavalry Charge.

A team must not use the ‘Flying Wedge’ or the ‘Cavalry Charge’.
Sanction: Penalty kick at the place of the original infringement.

‘Flying Wedge’. The type of attack known as a ‘Flying Wedge’ usually happens near the goal line, when the attacking team is awarded a penalty kick or free kick.

The kicker tap-kicks the ball and starts the attack, either by driving towards the goal line or by passing to a team-mate who drives forward. Immediately, team mates bind on each side of the ball carrier in a wedge formation. Often one or more of these team mates is in front of the ball carrier. A ‘Flying Wedge’ is illegal.
Sanction: Penalty kick at the place of the original infringement.

‘Cavalry Charge’. The type of attack known as as a 'Cavalry Charge' usually happens near the goal line, when the attacking team is awarded a penalty kick or free kick. Either a single player stands some distance behind the kicker, or attacking players form a line across the field some distance behind the kicker.

These attacking players are usually a metre or two apart. At a signal from the kicker, they charge forward. When they get near, the kicker tap-kicks the ball and passes to a player who had started some distance behind the kicker.
Sanction: Penalty kick at the place of infringement

(q) Advantage may be played for acts of foul play, but if the offence prevents a probable try, a penalty try must be awarded.

(r) For an offence reported by an assistant referee a penalty kick may be awarded where the offence occurred, or advantage may be played.

(s) All players must respect the authority of the referee. They must not dispute the referee’s decisions. They must stop playing at once when the referee blows the whistle except at a kick-off or at a penalty kick following admonishment, temporary suspension, or send-off.
Sanction: Penalty kick

I would say anything cycnical but not dirty is a professional foul.Holding a guys leg so he can't get up to make a tackle and obvious offside,hands in the ruck etc. where quick ball means an almost certain try.High or late tackles are just foul play and generally come about because a player loses their cool but to me professional implies that the offense is done with a cool detachment.

Professional foul - you purposely break the rules in order to disrupt the opposition and prevent conceding ground/possession/points.

Standard foul - you play on the grey area of the law between right and wrong.

Professional foul suggests a degree of intent and premeditation, weighing up that the punishment is less than not committing the crime. One of the primary things cards were first bough in for ( alongside dangerous play) was to deal with increasing incidences of players deciding to commit penalties rather than concede tries.

I can see that deliberately seeking to "rough up" an opponent could fit into this.
It is however quite possible to do that legally, find the video of the Tuillagi brothers targeting Abendanon till hes taken off in a Tigers/Bath game a couple of years ago with legal but viscous tackles.

Its also dangerous foul play as defined in the laws.

The term "Professional foul" is a rugby league term, and is defined in the laws of Rugby League as:
 
"A professional Foul is a deliberate act of foul play, usually to prevent an opponent from scoring"
 
 I cannot recall the words professional and foul ever being mentioned in sequence in the laws of Rugby Union, but I will bow down to the many thousands on here who are more knowledgeable of the laws of rugby Union than me.