Context. We analyze spectropolarimetric data taken with the Hinode spacecraft in quiet solar regions at the disk center. Distorted redshifted Stokes V profiles are found that show a characteristic evolution that always follows the same sequence of phases. Aims: We aim to characterize the statistical properties of these events and recover the stratification of the relevant physical quantities to understand the nature of the mechanism behind them. Methods: We studied the statistical properties of these events using spectropolarimetric data from Hinode/SP. We also examined the upper photosphere and the low chromosphere using Mg i b2 and Ca ii h data from Hinode. Finally, we applied the SIRGAUSS inversion code to the polarimetric data to infer the atmospheric stratification of the physical parameters. We also obtained these physical parameters taking into account dynamical terms in the equation of motion. Results: The Stokes V profiles display a bump that evolves in four different time steps, and the total process lasts 108 seconds. The Stokes I shows a strongly bent red wing and the continuum signal exhibits a bright point inside an intergranular lane. This bright point is correlated with a strong redshift in the Mg i b2 line and a bright feature in Ca ii h images. The model obtained from the inversion of the Stokes profiles is hotter than the average quiet-Sun model, with a vertical magnetic field configuration and field strengths in the range of kG values. It also presents a line of sight velocity stratification with a Gaussian perturbation, the center of which is moving to deeper layers with time. The Gaussian perturbation is also found in the gas pressure and density stratification obtained taking into account dynamical terms in the equation of motion. Conclusions: We have examined a particular type of event that can be described as a plasmoid of hot plasma that is moving downward from the top of the photosphere, placed over intergranular lanes and always related to strong magnetic field concentrations. We argue that the origin of this plasmoid might be magnetic reconnection that is taking place in the chromosphere. Appendix A is available in electronic form at http://www.aanda.org