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coach, my catcher catches mid/hi 90's to 101, and your prob is not uncommon -
#1 - don't expect long life from a catcher's glove as pitching gets better - and don't try to get extra life without some maintanence/rebuilding
get the best glove you can, and/or add support internally in the thumb area of the one you have (it's not a wilson pudge is it? they'll kill ya with floppy thumbs/no support) see "Gloveman" on this site for recommendation
**that support can be fashioned by a casting plastic known as "orthoprene" around the thumb, or modified internally by taking apart the glove, even new ones!
don't let your catcher catch "new pitchers" at game speed till he gets accustomed to their fb's movement in the bullpen (bad news at showcases)
if the pitcher throws a 2 seam & 4 seam fb, the catcher has to know which is coming
good luck
lefties? - - - they just aint right!