  An anomalous nuclear modification was reported by JLab measurements on the
beryllium-9 structure function F_2. It is unexpected in the sense that a
nuclear modification slope is too large to be expected from its average nuclear
density. We investigated whether it is explained by a nuclear clustering
configuration in Be-9 with two \alpha nuclei and surrounding neutron clouds.
Such clustering aspects are studied by using antisymmetrized molecular dynamics
(AMD) and also by a simple shell model for comparison. We consider that nuclear
structure functions F_2^A consist of a mean conventional part and a remaining
one depending on the maximum local density. The first mean part does not show a
significant cluster effect on F_2. However, we propose that the remaining one
could explain the anonymous JLab slope, and it is associated with high
densities created by the cluster formation in Be-9. The JLab measurement is
possibly the first signature of clustering effects in high-energy nuclear
reactions. A responsible physics could be an internal nucleon modification,
which is caused by the high densities due to the cluster configuration.
