I saw this video of a player slide tackling his teammate.
What are the rules on players tackling their own teammates like that?
Would it just be to show fair play and kick the ball out to treat the player?
(The situation explain in this answer assumes action against a teammate which involve misconduct and wouldn't be only foul. See this answer)
Can football players be penalised for an action against a teammate that is normally a foul if done to the opponent?
(Answer is no, for an action against a teammate that is normally a foul if done to the opponent.)
In short yes, laws of the game allows it.
From IFAB Laws of The Game :
Law 12 fouls and misconducts (emphasis added)
A player who commits a cautionable or sending-off offence, either on or off the field of play, against an opponent, a team-mate, a match official or any other person or the Laws of the Game, is disciplined according to the offence.
If the ball is in play and a player commits an offence inside the field of play against:
- a team-mate, substitute, substituted or sent off player, team official or a match official – a direct free kick or penalty kick
From FAQ of Law 12
Q6: Why is an offence against someone who is not an opponent now a direct free kick? Does this include dissent/offensive language?
If, for example, a player strikes a team-mate, substitute, team official or, perhaps even worse, a match official this is serious but only restarting with an IDFK suggested that the offence was not serious so it is now a direct free kick for any offence (directly) against anyone (except an opponent). This does not include dissent/offensive language etc. as this is not a direct/physical offence against a person (see below).
Q7: What is the restart of the referee stops play for dissent/offensive language etc.?
If the referee stops play to penalise a player for dissent/offensive language etc. the restart is an IDFK.
In 1994, Hearts teammates Graeme Hogg and current Hearts manager Craig Levein were sent off for scrapping during a pre-season friendly against Raith Rovers. Source
Update: From the IFAB Glossary
To punish, usually by stopping play and awarding a free kick or penalty kick to the opposing team
For Violent Conduct player can be sent-off. (see: SENDING-OFF OFFENCES)
Violent conduct is when a player uses or attempts to use excessive force or brutality against an opponent when not challenging for the ball, or against a team-mate, team official, match official, spectator or any other person, regardless of whether contact is made.
In addition, a player who, when not challenging for the ball, deliberately strikes an opponent or any other person on the head or face with the hand or arm, is guilty of violent conduct unless the force used was negligible.
However for the mention case, where Jack Hendry of Dundee tackles his own team-mate Cammy Kerr in a match against Rangers which they lost 4-1, I could not find anything that happened after the incident but I'm sure that Jack did not get booked.
No, a player cannot be penalised for an action against a teammate that is normally (only) a foul if done to the opponent.
Most free kick offences listed in Law 12 under direct free kicks and indirect free kicks that involve physicality against another player (e.g. a careless trip or tackle, or impeding) contain the wording "against an opponent", either directly in the wording of the offence, or in its definition (e.g. playing in a dangerous manner), meaning they cannot be committed against a teammate.
The only exception to this would be if the action was reckless or excessive enough to make it misconduct (i.e. a cautionable or sending-off offence) This free-kick offence is listed in Law 12 - Fouls and Misconduct, Section 2 - Indirect Free Kick:
An indirect free kick is awarded if a player:
- commits any other offence, not mentioned in the Laws, for which play is stopped to caution or send off a player
Note that there is no requirement for this offence to be committed against an opponent. This would include committing violent conduct (i.e. using excessive force) or unsporting behaviour (i.e. recklessness) against a teammate.
For these offences, after the offender is either cautioned or sent off, the restart would be upgraded from an indirect free kick offence to a direct free kick offence as per Law 12 - Fouls and Misconduct, Section 4 - Restart of Play After Fouls and Misconduct and Q6 & Q7 of Law 12 FAQ.