One of my favorite past times is observing behavior of free-range chickens and the group activities rank very high in this.

I have seen many times juveniles in engage in team aggression against a common foe. Sometimes the foe is an individual but usually it is against another group. Conflicts are usually over quality forage areas or feeder but can also involve loafing areas. Most conflict is in the form of display but is does occasionally come to blows. Outcome is usually determined by which group is made up of larger individuals although if group of smaller birds has more members, especially when in core of their home range, then size is not as important. Adults can greatly impact outcome especially if they act on behalf of one group or the other which can happen. The duration of such conflicts is so short that I have not managed to film it yet but I have gotten lucky and found very similar conflicts involving other species taking on adult chickens. Language and strategy appears very similar to what juvenile chickens do. What is interesting is how effectively aggression is reserved for foe and how much display is involved.

See following linked videos for examples I found with minimal looking.
Juvenile peafowl taking on a large sized cock of some sort.

Turkey (juveniles?) taking on an Aseel cock

Example showing Aseel juveniles attacking a larger juvenile chicken. Display component was sadly omitted and battle involves much more contact than I feel is natural.