Lead is a metal.
Malleability, which is the property of being deformed under large pressure into sheets without breaking, is typical of metals. Metals are also ductile, which mean thaty they can be formed into wires.
Both properties, malleability and ducitility of metals, are explained in terms of the metallic bond.
The metallic bond is the union that the metal atoms can form in virtue of the capacity of the valence electrons to move freely along a a large chain of atoms.
This freely motion of the valence electrons among a large chain of atoms, permits that, under a deforming force (stress) the atoms can roll over each other into new positions without breaking the metallic bond.
When the stress is large enough the metal piece will experience a permanent change of form, i.e. into a flat sheet, in the case of pounding, or into an elongated wire, in the case of a stretching force.