An efficient front crawl stroke helps propel the swimmer. The stroke in the freestyle should follow a curved path as shown in the figure, not exactly straight back. And also the angle of attack of the hand relative to the movement of the body must constantly change – this provides maximum lift to move forward.
Crawl stroke technique

While inserting and grabbing water with the hand, the elbow is above the brush. Further, the angle of flexion of the arm in the elbow joint, in the middle of the stroke, becomes maximum, approximately 90°. After entering the water, the hand performs a short rowing motion down and out to the width of the shoulder, then moves straight back, then powerfully accelerates along a curvilinear trajectory until the end of the stroke. This acceleration plays an important role in propulsion during the stroke. At the moment of accelerating the movement of the brush of one hand, the other slides forward and prepares to capture at a much lower speed, because it must thinly and accurately “cut” the flow of water. If the initial phase of the stroke is performed faster, then the created “amount” of movement and the effect of translational movement will be leveled. Fine coordination of hand movements is associated with the unhurried insertion of one hand into the water and a significant acceleration of the movement of the other at the end of the stroke. The body rotates equally in both directions around the longitudinal axis of the body.
Pace and stroke stroke in crawl (Frequency and length)

The frequency and length of the stroke in the freestyle determine the swimming speed. High-class swimmers perform fast and long strokes. Previously, it was believed that a high pace was necessary to achieve high speed, but Louis de B. Handley (1928) showed that a high stroke rate does not always contribute to swimming speed. Even more than 70 years ago, the famous Johnny Weismuller performed fewer strokes at a competitive distance than his rivals. His trainer William Bahrak rightly believed that infrequent strokes provided more powerful repulsion. And Weismüller himself noted that the secret of combining a low stroke rate with a high swimming speed is that a somewhat slow start of the stroke allows you to gradually increase its power.
Swimming speed in men is greater than in women, precisely due to the greater length of strokes, and their stroke frequency is almost the same.
Transition of one stroke to the beginning another

Очень важен переход от завершения одного гребка к началу another. Smooth alternating changes in body position in accordance with the coordination of strokes provide minimal resistance to progress. At this point, the swimmer must control the degree of rotation of the torso, the position of the arm and the speed of its passage in order to ensure a smooth and gradual lateral tilt (roll).
Hand position at the time of insertion

Hand position at the time of insertion при плавании кролем на груди очень важно с точки зрения обтекаемости. When swimming in a front crawl, the hand enters the water smoothly and separates the water flows, thereby reducing drag by moving them away from the swimmer’s head and shoulders.