What are the Physical effects of rugby on the body?

It you are talking pressure as in stress -- yes . Like all occupations a play is expected to perform for the 80 minutes they are on the pitch. When doing well players react well because their mood is high. When games are being lost pressure is brought on by the potential of being dropped, take out of the squad, replaced or in some instances transferred or plain sacked.

When that pressure is on the player can lose focus on the job in hand and try to "go it alone". This means that team mates see mistakes, passes not ,ade, essential kicks being missed as the concentration move from the game to the "what if I dont get this done,".