Self-handicapping in play:

"Larger, older, or more socially dominant animals do not use their full strength in play with smaller, younger, or more socially subordinate animals, and they seem to modify their strength and skill to match that of their partner."

"One consequence of self-handicapping is that dominance distinctions are less evident in play than in other contexts."

"The term 'self-handicapping' denotes that an animal's behavior reduces its probability of achieving its tactical objective in play and thereby prolongs the play interaction. Such behavior appears inconsistent with the statement that animals seek to win playfights. Loizo's dominant chimpanzee initiated a playfight by fleeing from its subordinate; ..."

Robert Fagen - Animal Play Behavior

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"Effort restriction: An animal restricts their strength, skills, or social potential while playing with a partner and does not use their full power during the play interaction. This includes role reversals in which the animal with superior abilities assumes the role of the weaker or losing partner. For instance, a stronger animal allows a weaker one to chase."

Milada Petru et al. - Revisiting Play Elements and Self-Handicapping in Play

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"In social interactions, animals can self-handicap by using positions and movements that impair their competitive ability and enable their playmates to gain the "attack" position. For example, they may inhibit the force of their bites and pushes, and allow themselves to be pushed over and chased, even when they have the ability to harm or dominate a playmate. They may also put themselves at a self-induced disadvantage by playing with larger, stronger, or more experienced play partners, or even with animals of a different species. Because play is only performed when its costs remain low, however, there is an upper limit of unpredictability and loss of control above which animals will not play." 

Marek Spinka et al. - Mammalian Play: Training for the Unexpected