Balled shot is when several pellets in a shotshell load are fused together during firing by propellant gases leaking past the wad while the shot is still in the barrel.

related:

• shot, fused

Footnotes / Sources:

“Glossary ⇒.”ﾠSporting Arms and Ammunition Manufacturers’ Institute.ﾠEd. SAAMI’s Technical Committee. Web. 15-18 Jan. 2011.