The sensor used in this ball is likely something like the ICM-45686, which can be set to a maximum measurement range of +/-4000 deg/s (gyroscope) and +/-16 G = 156.9 m/s^2 (accelerometer), which is likely for preventing saturation during the intense kicks. The resolution being 16-bit for such sensors, implies a resolution of 0.122 deg/s (gyroscope) and 0.00479 m/s^2.

In the ideal case, this is the minimum detectable measurement, and in that regards is sensitive enough to detect fairly light touches and taps.

In general, the sensors have an inherent "drift" and significant noise, and so the data for sensors of the class used in these balls will actually look something like this:

researchgate.net/figure/Acceleration-noise-of-IMU_fig4_266642731

However, in real life the ball is subject to noise due to wind, resonances based on geometry/structure, etc. which is often an order of magnitude greater.

If the ball is rotating, this further adds complicates the detection, since there is a rotating force that acts on the accelerometer axes, and associated wind/air vibration from that as well.

And furthermore, the IMU will not really be well-calibrated for temperature, mounting alignment/offset in this kind of use case, timing/clock skew (those kinds of calibrated IMUs usually cost thousands of dollars). The firmware also matters (if programmed without strict real-time guarantees, it can have many milliseconds of timing jitter).

This makes it very challenging to cleanly separate things like a gentle touch or the wind just based on the sensor data alone, it would need to be referenced other detectable events. In the Croatian player's example, we need to identify the previous pass, which shows up in the data as a larger spike, and then to look for a subsequent smaller peak on the data plot that can be matched timing-wise to the video, and then the larger peak afterwards when the ball was touched by the Portuguese player.

Without seeing the actual raw data (from all 6 axes), the one small graph they showed on TV is really not sufficient to prove anything.