Thanks got it to work somehow with get_user_velocity( id, ... ); vector_length( ... );

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Another question is it possible to keep another player in front of another player by some units ? Like charger from l4d for example. Right now I used velocity but if one player gets stuck while the carried player moves forward.
PHP Code:
if( ( flags & ( FL_ONGROUND | FL_PARTIALGROUND | FL_INWATER | FL_CONVEYOR | FL_FLOAT ) ) ) {
new lookOrigin[ 3 ], Float: lookOriginF[ 3 ], Float: sprVel[ 3 ];
get_user_origin( id, lookOrigin, 3 );
lookOriginF[ 0 ] = float( lookOrigin[ 0 ] );
lookOriginF[ 1 ] = float( lookOrigin[ 1 ] );
lookOriginF[ 2 ] = float( lookOrigin[ 2 ] );
get_velocity_to_origin( id, lookOriginF, get_pcvar_float( g_cvars[ SPRINT_SPEED ] ), sprVel );
sprVel[ 2 ] = 0.0;
set_pev( id, pev_velocity, sprVel );
if( g_player[ id ][ grabbed_victim ] )
set_pev( g_player[ id ][ grabbed_victim ], pev_velocity, sprVel );
g_player[ id ][ startedSprinting ] = true;
}