responsible for it?

In a defensive battle it is all-important that the general in command
should hold his troops well in hand, especially when the movements of
the enemy can be concealed by the terrain. The enemy is allowed his
choice of massing for an attack on any given point: so that the ability
to concentrate reserve troops on any threatened point is an
indispensable element of safety. It may be assumed that Hooker was,
at the moment of Jackson's attack, actually taking the offensive.
But on this hypothesis, the feebleness of his advance is still more
worthy of criticism. For Jackson was first attacked by Sickles as early
as nine A.M.; and it was six P.M. before the latter was ready to move
upon the enemy in force. Such tardiness as this could never win a
battle.

While all this had been transpiring on the right, Lee, to keep his
opponent busy, and prevent his sending re-enforcements to the flank
Jackson was thus threatening, had been continually tapping at the lines
in his front. But, owing to the small force left with him, he confined
this work to Hooker's centre, where he rightly divined his headquarters
to be. About seven A.M. the clearing at Chancellorsville was shelled by
some of Anderson's batteries, obliging the trains there parked to go to
the rear into the woods.

Hancock states that the enemy frequently opened with artillery, and made
infantry assaults on his advanced line of rifle-pits, but was always
handsomely repulsed. "During the sharp contests of that day, the enemy
was never able to reach my principal line of battle, so stoutly and
successfully did Col. Miles (who commanded the advanced line) contest
the ground."