GettyChristy Martin's happy Sydney Sweeney's lacing up her boxing gloves ... saying she's thrilled Syd's playing her in a new biopic, and she wants to make sure her ring moves look authentic.
The boxing legend tells TMZ ... she's excited for Syd's performance, especially because she has a background in MMA and combat sports -- and says the actor's performance can prove dynamite comes in small packages!
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