Help with pitching to lefty batters

Now that my baseball season is pretty much over for the rest of the year (actual organized games) me and two of my friends go down to the field and practice pitching to each other, being im a righty, one is a swich hitter and one is a lefty.
Now that you have that info let me ask my real question. How can i pitch to the lefty batter to get him out now that i am pitch from sidearm arm angle and no matter what i try i can’t strike em’ out anymore

i have a fastball high 70s
curveball 11-5
slider (just learned it a few days ago but good progress so far)

please help me so i can practice for next season…thanks

Well with most lefties, their happy zone is inside and lowish. So try to pitch on the third base half of home plate. And try to stay up and not low. Also a two seamer or cutter could help a great deal.

my four seemer (because of sidearm) looks like a 2seamer, and a nasty one at that. Though i have a slider which is to similar to a cutter to really make a difference, in my opinion. But i like your location idea which is completely different to whatt i do which might have been the problem :? being i pitch inside and low to everybody mosttly

My pitching coach once told me: “Move the ball around—high, low, inside, outside, change speeds and stay away from the middle of the plate.” He said it was important to change the batter’s eye level to confuse and discombooberate him, and never to throw one twice or three times in the same place and at the same speed. He once told me a very amusing story about Johnny Mize to illustrate a point.
The Yankees were to play the Indians one night in Cleveland, and some sportswriter went looking for Mize but couldn’t find him. Finally Big Jawn was located in the Yankees’ locker room—practicing golf swings with a bat. GOLF swings, for crying out loud! When Mize was asked about that, he said simply, "Garcia’s pitching tonight."
Mike Garcia, often called the Big Bear, was a powerful righthander who gave the Yankees more trouble than the rest of the Indians’ starting staff put together. But—like most pitchers—he was a creature of habit, and his habit was to start off every batter he faced with a fast ball low and inside. He had been getting away with it. But in this particular game the Yankees came to bat and put two runners on base. Mize stepped up to the plate, and Garcia, of course, fired his first pitch in there—yep, you guessed it, a fast ball low and inside. Mize was ready for it; he swung and golfed that pitch way back into the right field seats for a three-run homer and a lead which the Yankees never relinquished.
You can be sure he never saw another fast ball, in that location or anywhere else, from Garcia for the rest of the game. Q.E.D.—you have to know the hitters and how to pitch to them. And where. 8)

I would highly recommend the change-up. That pitch is a difference maker when facing someone opposite your pitching arm side. You’re a righty, it will be effective against lefties down and away. Same for lefties on righties.

Yeah i was thinking about learning a change up, but im learning a slider right now and i want to focus on that for a while, but what change up would you advise to learn after?

Take Zita’s advice and just move the ball around, no matter what side the batter hits from if you move the ball around and mix speeds you should be able to get outs. In general a lefty likes down and in from a righty (being a lefty myself) and what I had the hardest time with as a lefty facing righties was always the up and away pitch.

ok i will. It prob doesnt help that the lefty i pitch against most is a co-mvp in my rec league ( along with me) but ok moving the ball around and staying low and in is the hardest