when your in your off season is lifting lighter weights and more reps gonna give you more velocity for the upcoming seson then lifting heavier weights
if you lift , stay with the lower body more, your velocity will rise quickly after getting your legs stronger to push off the mound...
are deadlifts squats ab workouts leg extensions are those good
yes, dont go all out every time about twice a month you can do your max other than that i would work on reps...atleast 8 reps when not going for max...and yes all those would help eventually
Drop the leg extensions and throw in some pylometrics.