When using a security company, a business or event manager wants to ensure not only the safety and security of their property and anyone using it but also wants to ensure that any force used is reasonable, proportionate and legal.
Private security uses staff that have an appropriate SIA licence for the particular activities they are undertaking, which typically is worn by security personnel on their person at all times so they can be identified.
As part of this training, they are informed of what they can and cannot legally do in certain situations, and when force is deemed to be necessary, reasonable and proportionate to the situation.
Typically, security staff have the right to use reasonable force for the same reasons a civilian would, which includes self-defence, defending another person, defending property, preventing a crime and performing a lawful arrest.
Generally, security staff are allowed to issue verbal warnings, request for someone to vacate the premises in question, request ID, refuse entry to people who are not of sound mind, are acting aggressive or are not in compliance with the policies of the event, protect bystanders, break up fights and contact the police.
A member of security can also remove someone who refuses to leave when asked to do so. According to SIA guidelines, such a person becomes a trespasser, and trespassers can be removed using only the level of force necessary to do so.
They can, if required, respond to attacks with equal force if and only if it is necessary, but generally security staff are trained in conflict resolution and avoiding force wherever possible.
Most of the time, the presence of security is enough to ensure the safety and security of a venue, and most bad actors are identified swiftly and dealt with accordingly using only the force that is required to do so.