  Let B be a p-block of the finite group G. We observe that the p-fusion of G
constrains the module structure of B: Any basis of B that is invariant under
the left and right multiplications of a chosen Sylow p-subgroup S of G must in
fact form a semicharacteristic biset for the fusion system on S induced by G.
The parameterization of such semicharacteristic bisets can then be applied to
relate the module structure and defect theory of B.
