  We study a capacity theory based on a definition of Haj{\l} asz-Besov
functions. We prove several properties of this capacity in the general setting
of a metric space equipped with a doubling measure. The main results of the
paper are lower bound and upper bound estimates for the capacity in terms of a
modified Netrusov-Hausdorff content. Important tools are $\gamma$-medians, for
which we also prove a new version of a Poincar\'e type inequality.
