In this game, the player, who keeps a cool head, wins.
or
In this game, the player who keeps a cool head wins.
when to use comma before who and when not to use comma before who?
In this game, the player, who keeps a cool head, wins.
or
In this game, the player who keeps a cool head wins.
when to use comma before who and when not to use comma before who?
In your sentences
In this game, the player, who keeps a cool head, wins.
emphasis is on keeping a cool headIn this game, the player who keeps a cool head, wins.
emphasis is on playerIn this game, the player who keeps a cool head wins.
emphasis is on wins
Who keeps a cool head is a subordinate clause modifying player, so being offset by commas is appropriate but not necessary.
In this game as the initial phrase, using a comma is appropriate.
The main gist of the sentence
The player ... wins
is the independent clause.
Also appropriate might be
In this game, whoever keeps a cool head wins.
In this game, the player, who keeps a cool head, wins.
The sentence means In this game, the player wins
. The who keeps a cool head
is parenthetical and is extra information telling you that the player referred to keeps a cool head.
In this game, the player who keeps a cool head, wins.
This means that all players who keep cool heads will win.