The phrase "big mismatch" means that there is a significant difference or discrepancy between two things that should be similar or compatible.
Sentences with «big mismatch»
Ramsey against Vidal second big mismatch (not matching him against costa as that would be unfair to the lad as he is not a winger) (justarsenal.com)
Thus comparisons to model simulations (which generally estimate an impact comparable to that of Pinatubo in 1991) showed a pretty big mismatch (see Hansen et al (2007)-RRB-. (realclimate.org)
Missed it, but looking at the result, it seems like Ritson - Cardle was as big a mismatch as I thought it would be. (sbnation.com)