Only acts of foul play can invoke a penalty try, it was changed about 5-6 years back. Things like high tackles and deliberate pushing of a player without the ball.
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That's not my understanding, or reading of the rules. The Mark Tookey try, and the penalty try this year, were both penalty tries for professional fouls. the Ainscough try was for an act of foul play, but is was also a professional foul at the same time in that it prevented the player from contesting.
The rules actually say:
Penalty try (d) the Referee may award a penalty try if, in his
opinion, a try would have been scored but for the
unfair play of the defending team. A penalty try is
awarded between the goal posts irrespective of
where the offence occurred.
I think the reference to foul play you are thinking of may be the penalty for foul play in the act of a player scoring a try, which gives the referr the right to give a penalty kick from in front in addition to the conversion attempt (the 8 point try).