In transport, a trace is one of two, or more, straps, ropes or chains by which a carriage or wagon, or the like, is drawn by a harness horse or other draught animal. The once popular idiom: "kick over the traces" comes from a frisky animal kicking one or both feet outside a trace. Unable to understand the entanglement, the animal may become wildly confused and out of control, possibly even breaking away. Hence, to "kick over the traces", when referencing a person, means to become wild and uncontrollable.
References
Trace (tack) Wikipedia(Text) CC BY-SA