Mass. Gen. Laws ch. 106, § 2A-504
(3) If the lessor justifiably withholds or stops delivery of goods because of the lessee's default or insolvency (Section 2A–525 or 2A–526), the lessee is entitled to restitution of any amount by which the sum of his payment exceeds:
(4) A lessee's right to restitution under subsection (3) is subject to offset to the extent the lessor establishes: