  The transfer of football players is an important part in football games. Most
studies on the transfer of football players focus on the transfer system and
transfer fees but not on the transfer behavior itself. Based on the 470,792
transfer records from 1990 to 2016 among 23,605 football clubs in 206 countries
and regions, we construct a directed footballer transfer network (FTN), where
the nodes are the football clubs and the links correspond to the footballer
transfers. A systemic analysis is conduced on the topological properties of the
FTN. We find that the in-degrees, out-degrees, in-strengths and out-strengths
of nodes follow bimodal distributions (a power law with exponential decay),
while the distribution of link weights has a power-law tail. We further figure
out the correlations between node degrees, node strengths and link weights. We
also investigate the general characteristics of different measures of network
centrality. Our network analysis of the global footballer transfer market sheds
new lights into the investigation of the characteristics of transfer
activities.
