The phrase "horrendous mistake" means a very terrible or awful error that was made.
Sentences with «horrendous mistake»
Cech is finished, Ospina has really only made on horrendous mistake. (justarsenal.com)
So everyone forgets the two horrendous mistakes tarks made in the first half which allowed Everton chances... (uptheclarets.com)
The Poland international was ousted from Arsenal starting XI midway into last season by David Ospina after series of horrendous mistakes. (theclockend.com)