How to Do a Straddle Split
Before you perform a straddle split, warm up by stretching your leg muscles to avoid injuring yourself. When you're warmed up, lay flat on your back with your legs up and your butt against the wall. Then, stretch your legs out to your sides in a "V" shape, but don't go so far that you feel pain. After you've done the splits in this position, try standing up with your feet shoulder width apart. Next, slowly lower your butt towards the floor as you push your feet outwards. Once your legs feel tight, hold the position and breathe for 10-15 seconds.
Warm up. It is important to warm up your muscles and stretch to ensure that you do not injure yourself. You must especially stretch and warm up your legs and back as they will be primarily involved in performing the straddle splits. Position yourself against a wall. Lay on your back with your legs in the air and your butt against a wall. Keep your back straight and flat as your press against the wall for support. Wear comfortable clothing and shoes for mobility and traction. Lay on a mat or pillow if the ground is uncomfortable for your back. You will need shoes with good traction in order to walk your legs out across the wall. Walk your legs out. Slowly drop your legs to each side of you along the wall in a “V” shape”. Spread your legs apart until they are tight but not far enough that you feel pain. Hold the V pose for 10-15 seconds. Move to a standing position. Once you have practiced the V position against a wall, stand comfortably with your feet shoulder-width apart and bent over at the hip. This is best done on tile or hardwood but make sure that the floor isn't too slippery. Practicing barefoot may help you slide along the floor whereas socks may be too slippery and cause injury. Push your feet outwards. Using a slow and controlled movement, slide your feet outwards, and lower your butt towards the ground. Take your time and use your arms to steady yourself. If you find your feet slipping, try wearing shoes or practicing on a rubber mat. If you feel you can't get as far as you like, use a chair in front of you or practice in front of a wall to stabilize your body. Point your toes out and upward towards the sky. You should not let the tops of your feet turn in if you can help it. Stop when it becomes tight. Once you've reached the furthest angle of your splits, hold the pose and breathe as you hold 10-15 seconds. Work your way back up to the starting stance slowly to make sure you don't injure yourself. Roll your hip downwards to inch further down. This keeps your stomach towards the ground as your legs continue to spread. For a greater stretch, roll your hip backwards to turn out your legs. This is difficult but gives your hips a deeper stretch. Practice as much as you can. Straddle splits take time to master as you need to increase your flexibility. Remember to always warm up before you practice and only push yourself as much as your body will allow. Go slowly and utilize proper movements to make sure you don't injure yourself.  Working on this pose daily can help you get into a full straddle split. Aim to do the straddle stretch for approximately 3 to 5 minutes per day. Perform cardio exercises. It's important to warm up your muscles before getting into the splits. Perform about 15 minutes of cardio to warm up your muscles. There are many options for cardio so do what you enjoy so you don't get bored by the repetition. Whether you enjoy jumping jacks, climbing stairs, or jogging, get your muscles to loosen up and slowly work them up to more vigorous movements. Increase the intensity of your warm up with jump rope, squats, or box jumps to get your blood flowing in your legs. Stretch your back. Form a bridge by lying with your back on the floor and trying to push yourself up on your feet and hands. Your knees should be bent with your palms and feet planted on the ground. You should try to form a bridge by lifting your back as far from the ground as you can by pushing down through your feet and hands. Point your elbows to the ceiling and feel your back stretch. It may be difficult at first but with time and practice your flexibility will increase. Don't force anything if you start to feel pain. Push yourself to feel a stretch but don't push so far that you feel pain. Stretch your lower body. Use the runner's stretch for your lower body. Get into the lunge position by taking a step forward. Bring your fingertips as low as you can. Raise your butt by slowly straightening your front leg. Inhale as you straighten your leg. Feel your front leg stretch and exhale. Get back into the starting lunge position and repeat. Repeat the runners stretch for both legs, repeating 4x per leg. Stretch your upper body. Perform a standing side stretch by reaching over your head, grip your fingers together but extend your pointer fingers and keep them together. Stretch and inhale as you get as long as you can while bending to one side. Take a deep and slow breath as you hold your pose for 5 seconds then return to a tall, standing position with your arms above your head. Make sure to perform the standing side stretch on both sides of your body. Practice the frog pose. Open deep muscles in your inner thighs with this pose. Start on all fours, rest on your forearms instead of your hands, and lower your pelvis and hips by slowly spreading your knees apart. Make sure to use control and breathe deeply as you lower yourself. Feel the stretch and don't go over your capacity. Once you feel a stretch, hold the pose and take 10 - 15 breaths. Get into the butterfly pose. This pose is great for working toward the straddle splits. Sit with a tall posture and the soles of your feet together with you knees dropping to your side. Inhale and exhale as you gently lower your knees. Don't force your knees down by feel the stretch. Once comfortable, slowly move your chest toward your feet, keeping your spine straight as your fold your body forward. Hold for 10 breaths. If your knees are high off of the ground, add some support under your seat so that your hips lift up off the floor. You want to release the tension on your hip flexors. Pancake yourself. Pancake pose is a high intensity pose. Sit up tall and keep your legs spread wide apart. Lengthen your spine by slowly lifting your chest. Flex your toes to create tension in your legs. Bring your chest to the floor as you move your fingertips in front of your pelvis and continue to walk them forward slowly. Keep your spine straight and only move as far as you feel the stretch. Take 10 - 15 breaths as you move further into the pose. Let gravity help you open your hips and legs in this pose so that your body becomes familiar with the movements of a straddle splits. Sit and straddle stretch. Sit with your legs as far apart as possible with your toes pointed but legs relaxed. Lean forward to stretch your hips over your hamstrings. Keep your lower back as flat as you can and avoid rounding it. Warm up with front splits (optional). If you have already tried front splits, you may use it to warm up. The front splits is a great way to develop hip and hamstring flexibility in order for you to move on to the straddle splits. 
Warm up. Position yourself against a wall. Walk your legs out. Move to a standing position. Push your feet outwards. Stop when it becomes tight. Practice as much as you can. Perform cardio exercises. Stretch your back. Stretch your lower body. Stretch your upper body. Practice the frog pose. Get into the butterfly pose. Pancake yourself. Sit and straddle stretch. Warm up with front splits (optional). 