The box-to-box 8 is the engine of the midfield. He arrives late into the attacking box, tracks back to cover when a full-back overlaps and wins second balls in midfield.
High aerobic capacity is mandatory, paired with decent passing, tackling and finishing — this is not a specialist but a generalist.
Steven Gerrard, Yaya Touré and Frank Lampard are the iconic examples; a good modern B2B creates a tactical asymmetry with a more creative partner.