It is the one foundation symptom that is genuinely time-sensitive. A block wall deflecting inward is being pushed by soil pressure it cannot carry, and unlike most settlement the failure mode is sudden rather than gradual.
More detail
Most foundation problems progress slowly enough that a few months of monitoring is reasonable. Bowing is the exception, and it is worth treating differently. The mechanism. Soil against the outside of a basement wall exerts lateral pressure. Saturated soil exerts far more, and clay that expands as it takes on water exerts more still. A block wall has little resistance to bending, so the pressure pushes it inward, usually cracking horizontally along a mortar joint near mid-height where the bending is greatest. How severity is measured. Deflection is the distance the wall has moved out of plumb, checked with a long straightedge or a plumb line from the top of the wall. Roughly, under an inch is monitored and often repairable with reinforcement, one to two inches usually calls for reinforcement now, and beyond that the options narrow toward rebuilding. A wall that is shearing at the top or bottom course, or where blocks have visibly displaced relative to each other, is beyond monitoring. Repair options by severity. Carbon fiber straps bonded to the interior face are the least invasive and are appropriate for walls with limited deflection that are not actively moving; they stop further movement but do not straighten. Steel I-beams anchored top and bottom carry more load. Wall anchors placed in the yard and tied through the wall can apply tension over time and in favorable conditions recover some deflection. Full rebuild is the last option and requires excavation. What to do immediately regardless. Reduce the water load, since saturated soil is what generates the pressure: extend downspouts, correct grading, and stop irrigating against that wall. Then get a structural evaluation rather than a repair quote, because these two are not the same conversation.